Travis config cleanups and move ObjC to Xcode 9.1.

Stop having travis build the test matrix and make it explicit so extra
settings are only on the test that need the, this helps make the travis
UI a little cleaner (linux hosted stuff doesn't list an Xcode version),
as well as avoid unneeded requirements limiting the travis pool something
can run on.

Small improvements to objectivec/DevTools/full_mac_build.sh to avoid some
repeated scripting and hopefully make things more reliable work with Xcode
9.x.

Don't mark the iOS tests as able to fail, hopefully with the new settings
they are stable and won't give false signals.

Simplify the case for xcode versions and fixup xcode 9.[0-1].

.travis.yml

-sudo: required
-dist: trusty
-# everything is driven by the test.sh, so the language doesn't really
+# Everything is driven by the test.sh, so the language doesn't really
 # matter, it just controls the default install/script/etc. steps on
 # travis.
 language: cpp
-os: osx
-osx_image: xcode8.3
-script:
-  - ./tests.sh $CONFIG
-env:
-  - CONFIG=cpp
-  - CONFIG=cpp_distcheck
-  # Testing go requires installing golang, currently travis.sh is doing that
-  #   with apt-get which doesn't work on OS X.
-  # It's nontrivial to programmatically install a new JDK from the command
-  #   line on OS X, so we rely on testing on Linux for Java code.
-  - CONFIG=javascript
-  # iOS build log was starting to choke travis UI, so split to cover the
-  # Xcode Debug and Release Configurations independently.
-  - CONFIG=objectivec_ios_debug
-  - CONFIG=objectivec_ios_release
-  - CONFIG=objectivec_osx
-  - CONFIG=objectivec_cocoapods_integration
-  - CONFIG=python
-  - CONFIG=python_cpp
-  - CONFIG=php5.6_mac
-  - CONFIG=php7.0_mac
+script: ./tests.sh $CONFIG
+
+# The test matrix is manually built to cover a mix of linux and macOS
+# hosted setups; this lets some extra settings be done specific to each
+# host/language instead of forcing common values on all the tests.
 matrix:
   include:
+    # -----------------------------------------------------------------
+    # macOS hosted tests for Objective-C
+
+    - os: osx
+      env: CONFIG=objectivec_osx
+      osx_image: xcode9.1
+      language: objective-c
+    # iOS build log was starting to choke travis UI, so split to cover the
+    # Xcode Debug and Release Configurations independently.
+    - os: osx
+      env: CONFIG=objectivec_ios_debug
+      osx_image: xcode9.1
+      language: objective-c
+    - os: osx
+      env: CONFIG=objectivec_ios_release
+      osx_image: xcode9.1
+      language: objective-c
+    - os: osx
+      env: CONFIG=objectivec_cocoapods_integration
+      osx_image: xcode9.1
+      language: objective-c
+
+    # -----------------------------------------------------------------
+    # macOS hosted tests for other languages.
+
+    - os: osx
+      env: CONFIG=cpp
+    - os: osx
+      env: CONFIG=cpp_distcheck
+    - os: osx
+      env: CONFIG=javascript
+    - os: osx
+      env: CONFIG=python
+    - os: osx
+      env: CONFIG=python_cpp
+    - os: osx
+      env: CONFIG=php5.6_mac
+      # Xcode versions force a host version of macOS:
+      #   https://docs.travis-ci.com/user/reference/osx/#OS-X-Version
+      # Force macOS 10.12, the default travis image is going to be
+      # updated "soon", at which point this came come out:
+      #   https://blog.travis-ci.com/2017-10-16-a-new-default-os-x-image-is-coming
+      osx_image: xcode8.3
+    - os: osx
+      env: CONFIG=php7.0_mac
+      # Same note about macOS version as on the php5.6_mac config.
+      osx_image: xcode8.3
+
+    # -----------------------------------------------------------------
+    # Linux hosted tests
+
     # The dotnet environment requires Ubuntu 14.04 or 16.04. This
     # configuration is effectively an "extra" one, outside the
     # autogenerated matrix.
@@ -35,6 +67,7 @@ matrix:
       env: CONFIG=csharp
       language: csharp
       dist: trusty
+      sudo: required
       dotnet: 1.0.1
       mono: none
     # This test is kept on travis because it doesn't play nicely with other
@@ -45,16 +78,14 @@ matrix:
     # fetch pre-built Linux protoc binaries in the test.
     - os: linux
       env: CONFIG=java_compatibility
+      sudo: required
+      dist: trusty
     # The Python compatibility test currently only runs on Linux because it will
     # fetch pre-built Linux protoc binaries in the test.
     - os: linux
       env: CONFIG=python_compatibility
-  allow_failures:
-    # Mark the iOS test as flakey as xcodebuild some times fails to start the
-    # iOS Simulator.
-    - os: osx
-      env: CONFIG=objectivec_ios_debug
-    - os: osx
-      env: CONFIG=objectivec_ios_release
+      sudo: required
+      dist: trusty
+
 notifications:
   email: false

objectivec/DevTools/full_mac_build.sh

@@ -253,36 +253,20 @@ if [[ "${DO_XCODE_IOS_TESTS}" == "yes" ]] ; then
       XCODEBUILD_TEST_BASE_IOS+=(
           -destination "platform=iOS Simulator,name=iPhone 4s,OS=9.0" # 32bit
           -destination "platform=iOS Simulator,name=iPhone 7,OS=10.0" # 64bit
-          -destination "platform=iOS Simulator,name=iPad 2,OS=9.0" # 32bit
-          -destination "platform=iOS Simulator,name=iPad Pro (9.7 inch),OS=10.0" # 64bit
       )
       ;;
-    8.1* )
-      XCODEBUILD_TEST_BASE_IOS+=(
-          -destination "platform=iOS Simulator,name=iPhone 4s,OS=8.1" # 32bit
-          -destination "platform=iOS Simulator,name=iPhone 7,OS=10.1" # 64bit
-          -destination "platform=iOS Simulator,name=iPad 2,OS=8.1" # 32bit
-          -destination "platform=iOS Simulator,name=iPad Pro (9.7 inch),OS=10.1" # 64bit
-      )
-      ;;
-    8.2* )
-      XCODEBUILD_TEST_BASE_IOS+=(
-          -destination "platform=iOS Simulator,name=iPhone 4s,OS=8.1" # 32bit
-          -destination "platform=iOS Simulator,name=iPhone 7,OS=10.2" # 64bit
-          -destination "platform=iOS Simulator,name=iPad 2,OS=8.1" # 32bit
-          -destination "platform=iOS Simulator,name=iPad Pro (9.7 inch),OS=10.2" # 64bit
-      )
-      ;;
-    8.3* )
+    8.[1-3]* )
       XCODEBUILD_TEST_BASE_IOS+=(
           -destination "platform=iOS Simulator,name=iPhone 4s,OS=8.1" # 32bit
           -destination "platform=iOS Simulator,name=iPhone 7,OS=latest" # 64bit
       )
       ;;
-    9.0* )
+    9.[0-1]* )
       XCODEBUILD_TEST_BASE_IOS+=(
           -destination "platform=iOS Simulator,name=iPhone 4s,OS=8.1" # 32bit
           -destination "platform=iOS Simulator,name=iPhone 7,OS=latest" # 64bit
+          # 9.0/9.1 both seem to often fail running destinations in parallel
+          -disable-concurrent-testing
       )
       ;;
     * )
@@ -299,7 +283,7 @@ if [[ "${DO_XCODE_IOS_TESTS}" == "yes" ]] ; then
     "${XCODEBUILD_TEST_BASE_IOS[@]}" -configuration Release test
   fi
   # Don't leave the simulator in the developer's face.
-  killall Simulator
+  killall Simulator 2> /dev/null || true
 fi
 if [[ "${DO_XCODE_OSX_TESTS}" == "yes" ]] ; then
   XCODEBUILD_TEST_BASE_OSX=(