Remove redundant docker files from grpc repo

Allow using service account credential for per_rpc_creds interop test.

Allow usable auth for JWT token creds interop test

Removing some unused vestiges

Fixing #3286

- We cannot use call_data after the final callback as this one may
  trigger the deletion of the call object (hence the call_data).

Interop test update

Backport of 0.11 to master

Remove check for no workers

I *believe* this is actually safe, and the assert was errantly
copy-pasted a while back.

Fixes #3022

Guard against empty vector

Final beta API cleanup

The gRPC protocol objects

Plumb protocol objects through RPC Framework core

(1) Renamed the "beta" module "implementations" because it hasn't been
monolithic since "interfaces" was factored out of it a few changes
back.

(2) Moved ChannelConnectivity from grpc.beta.beta to
grpc.beta.interfaces since it is constants that don't depend on the
beta implementation.

(3) Moved the Server interface definition from grpc.beta.beta to
grpc.beta.interfaces since it is an interface.

(4) Dropped the "create_" prefix from "create_<...>_channel" functions
to better match the other creation functions throughout the codebase.

Use service account credentials for per RPC test

Update interop tests

Fix a case where :status could be returned to applications

Update debian install instructions

Initial work on protocol objects

Fixing bad_client test.

Fixing lingering bytes clipping issue on socket shutdown.

Merging beta back to master

Fix compilation