Features included in this merge:
- Added script to build and upload docker image for matrix test.
- Added script to create test cases and created go__master testcases based on it.
- Created dictionary for runtimes and gRPC releases for supported languages.
- Added go 1.7 and 1.8 Dockerfile/templates.

See tools/interop_matrix/README.md for details.

This reverts commit 79759fea, reversing
changes made to dc36f4df.

docker on osx needs slightly different command line option

Change shebangs to `#!/usr/bin/env python` instead of
`#!/usr/bin/env python2.7`.

Update run_tests/*.py to use six based isomorphisms and print function
from __future__ module.

created separate class for Http2Server.

Add response parameters to custom_metadata streaming request for Node and PHP
clients.

The Java server does not respond with separate initial and trailing
metadata when there is no response data - it is only emiting the
requested trailing metadata. Adding the response parameters to the test
(in accordance with the specification) avoids this, but I will open a
separate issue to investigate the Java behavior.