Fix alpine build

Update Python interop tests to use google-auth package

Fix Flatbuffer compatibility issues

add artifact build jobs for internal_ci

Prevent out of disk space error on internal_ci

Documentation for writing unit tests for client-side sync APIs.

grpc_mpsc queue based completion queue

Eliminate grpc_cc_libraries

Best practice for Bazel builds gives one rule per target, and producing
multiple targets conflicts with this.

Short term: define macros, and common libraries that can eliminate the
duplication.

Longer term: eliminate the existing plugin registration mechanism, and
replace it with a C++ static initialization in appropriate files. This
will allow grpc to be layered strictly atop grpc_unsecure (and similarly
grpc++ atop grpc++_unsecure and grpc).

Revamp artifacts, packages and distribtests

Don't crate GRPC_OS_ERROR with a non-static string

Cleanup of the BUILD files.

Revert "Implement Server Backward Compatibility"

Implement Server Backward Compatibility

clang5 fixes

The oauth2client test dependency is still needed as it used by
the beta API unit tests.

Propagate deadline to GenericServerContext

Upgrade C# to protobuf 3.3.0