implement timeout_on_sleeping_server interop test

Let grpc target depend on //external:zlib

target like
https://github.com/google/kythe/blob/master/third_party/zlib/BUILD can
be pulled in.

Service-side read without allowance

Add health-checking to Python.

This compensates for the abstraction mismatch described in issue 2916.

Separate headers and trailers

Fixing type-o

generate auth URI for JWT access token properly

client code clean up

add external tag set API

Wraps the connectivity API

C client library auth: produce adequate error codes and messages.

Remove C++11 dependencies in QPS test that break old compilers

Grpc ruby enable propagation between calls

Node fix auth interop

small fix for go docker private image building

Adds the initial reference implementation for health-checking in gRPC
Python as a separate project (but within the same grpc package to keep
namespaces consistent). Only installs the package to test the
build-proto-modules custom command introduced in the health-checking
project.

Rename SingleValueHandler->SingleHandler, StreamHandler->EventHandler

Expose new core functionality to Python.

adding build.sh for go so that go can test with private changes and p…

fixing a go docker image build error.