(1) Move dependency on protobuf from grpcio to grpcio_test. While the
most-commonly-foreseen use case of grpcio makes use of protobuf,
technically protobuf is not strictly needed and there's no actual
in-code relationship between grpcio and protobuf.
(2) Loosen the dependency on protobuf from ==3.0.0a3 to >=3.0.0a3.
(3) Update all references to 0.10.0* to 0.11.0.
(4) Alphabetize the grpcio_test dependencies.
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.