CI: New Docker tests for Python with numpy (#5677)

* New Docker tests for Python with numpy

* print numpy status in test suite

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

+FROM python:2.7.15-slim-stretch as base
+WORKDIR /code
+ADD . .
+RUN cp flatc_debian_stretch flatc
+WORKDIR /code/tests
+RUN python --version
+RUN pip install numpy
+RUN pip install coverage
+RUN ./PythonTest.sh

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

+FROM python:3.7.1-slim-stretch as base
+WORKDIR /code
+ADD . .
+RUN cp flatc_debian_stretch flatc
+WORKDIR /code/tests
+RUN python --version
+RUN pip install numpy
+RUN pip install coverage
+RUN ./PythonTest.sh

tests/py_test.py

@@ -2368,6 +2368,13 @@ def main():
 
     kwargs = dict(argv=sys.argv[:-3])
 
+    # show whether numpy is present, as it changes the test logic:
+    try:
+        import numpy
+        print('numpy available')
+    except ImportError:
+        print('numpy not available')
+
     # run tests, and run some language comparison checks if needed:
     success = backward_compatible_run_tests(**kwargs)
     if success and os.environ.get('COMPARE_GENERATED_TO_GO', 0) == "1":