Manual upmerge from v1.0.x

Use thread pool from concurrent-ruby on ruby server

Support server-side streaming of a unary RPC

Move subchannel_call_holder code into client_channel module.

Improve gRPC CLI

Add ServerBuilderPlugin::UpdateChannelArguments

Add IWYU export pragmas to grpc++/grpc++.h.

Add no-logging test

server builder include fix

Add Trace context proto. This is used to transmit trace context between RPC client and server systems.

Use the VIP that routes to GFE.

prep work for enabling caching

Remove undefined env

Little bit improving code style and php docs

moved method computation in a if block only when send_initial_metadata
is true.

Rename Fail Fast doc to Wait for Ready

Change cq_verifier to report file and line number for expectations.

Adding extension points for security context.

response on a StreamedUnary

Avoid static initialization of the kIdentity block

modified comment about when GET verb is used.
Added code to read data from send_message and defer the op when
  it is not fully available.
clang-format one more time.

Updated protobuf to fix gmock url in autogen.sh