Rama/travis fixes fornow (#1272)

* Update Dockerfile

took out make -j 8 as we are running out of virtual memory.
added df -k for getting the disk space info in logs.

* Update .travis.yml

As we bring up 3 containers here i am reducing to 2 and trying to see if this is deployed on different  machines then should not matter.

* Update .travis.yml

3 in parallel should pass also 2 of then are passing so trying this out

.ci/travis/ubuntu/Dockerfile

@@ -30,7 +30,7 @@ RUN mkdir /root/ngraph/build
 WORKDIR /root/ngraph/build
 RUN cmake ../ -DNGRAPH_USE_PREBUILT_LLVM=TRUE -DCMAKE_INSTALL_PREFIX="~/ngraph_dist"
 RUN make style-check
-RUN make -j 8
+RUN make 
 RUN make install
 
 # Prepare nGraph Python API
@@ -40,5 +40,7 @@ ENV NGRAPH_CPP_BUILD_PATH /root/ngraph_dist
 ENV LD_LIBRARY_PATH /root/ngraph_dist/lib
 ENV PYBIND_HEADERS_PATH /root/ngraph/python/pybind11
 
+RUN df -k 
+
 # Test nGraph and nGraph Python API
 CMD cd /root/ngraph/build && make check ; cd /root/ngraph/python && tox