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.

Allow specifying DNS server to query for c-ares via URI authority.

Add trace protector to flag

Set Frame Size to Bytes per Microsecond

Fix minor problems in server backward compatibility

Make cq_verifier output more readable

Fix some races in tests

Add MacOS interop and UBSan C to internal CI

Add unary fullstack trickle to bm json

Blanket suppress protobuf from ubsan runs

C++ compatibility fixes

Implement grpclb drop support.

Upmerge v1.3.x branch to master

C#: Dont use non-blittable types in native method signatures

Fix runtests --force_default_poller on linux

Unref pending events under cq lock

Doxygen cpp nits

PHP: fix pecl extension version

PHP: fix pecl extension after cc files are added

Add Backward compatibility API to C++

Fixes to subchannel and its index

Fix hpack_size test

PHP: stop requiring google/protobuf PHP implementation