Adds coverage reports for C and C++.

Add run_interop.sh jenkins script

Improving the C# auth API

Latency profiling support

C++ code generator plugin: eliminate use of nullptr

external code compiled under gcc-4.4 : eliminate use of nullptr, primarily.

Avoid lock/unlock for common client channel pick.

Used the proper GRPC_TRACE value in run_tests.py

Stop using atm operations on fd->shutdown

Robustness work for port_server startup

Removing warnings when using boringssl.

within fd->mu anyway (and is not the right size for atm in some cases)

PHP: validate and normalize metadata keys

Give Python tests 15 minutes

Preinstall and cache dependencies in docker test runs

Fix issue with Node installation

Retry timeouts on pull requests