Docker tests for Zend PHP and Mono C#; Python coverage; TODO for HHVM PHP (#5125)

* Docker test for Zend PHP 7.3

* hhvm

* move failing hhvm test to TODO zone

* c# mono 5.18 test

* python coverage reports

tests/docker/TODO.Dockerfile.testing.php.hhvm_2019_01_16

+# This does not pass tests due to the following error:
+#
+# Fatal error: Uncaught exception 'InvalidArgumentException' with message 'Google\FlatBuffers\ByteBuffer::getX() expects parameter 1 by reference, but the call was not annotated with '&'. in /code/php/FlatbufferBuilder.php:971
+# Stack trace:
+# #0 /code/tests/phpTest.php(277): Google\FlatBuffers\FlatbufferBuilder->sizedByteArray()
+# #1 /code/tests/phpTest.php(79): fuzzTest1()
+# #2 /code/tests/phpTest.php(86): main()
+# #3 {main}
+#   thrown in in /code/php/FlatbufferBuilder.php:971
+FROM hhvm/hhvm:2019.01.16 as base
+WORKDIR /code
+ADD . .
+RUN cp flatc_debian_stretch flatc
+WORKDIR /code/tests
+RUN hhvm --version
+RUN hhvm phpTest.php
+RUN ../flatc --php -o php union_vector/union_vector.fbs
+RUN hhvm phpUnionVectorTest.php

tests/docker/languages/Dockerfile.testing.csharp.mono_5_18

+FROM mono:5.18 as base
+WORKDIR /code
+ADD . .
+RUN cp flatc_debian_stretch flatc
+WORKDIR /code/tests
+RUN mono --version
+WORKDIR /code/tests/FlatBuffers.Test
+RUN sh NetTest.sh

tests/docker/languages/Dockerfile.testing.php.zend_7_3

+FROM php:7.3-cli-stretch as base
+WORKDIR /code
+ADD . .
+RUN cp flatc_debian_stretch flatc
+WORKDIR /code/tests
+RUN php --version
+RUN php phpTest.php
+RUN sh phpUnionVectorTest.sh

tests/docker/languages/Dockerfile.testing.python.cpython_2_7_15

@@ -4,4 +4,5 @@ ADD . .
 RUN cp flatc_debian_stretch flatc
 WORKDIR /code/tests
 RUN python --version
+RUN pip install coverage
 RUN ./PythonTest.sh

tests/docker/languages/Dockerfile.testing.python.cpython_3_7_1

@@ -4,4 +4,5 @@ ADD . .
 RUN cp flatc_debian_stretch flatc
 WORKDIR /code/tests
 RUN python --version
+RUN pip install coverage
 RUN ./PythonTest.sh