-Rename namespace to grpc_health->grpc to match spec
-Proper use of NOT_FOUND status code
-Improve testing
-Add source distribution to artifact build

Source packages were not getting the necessary C files due to
`make_grpcio_tools.py` not being invoked before `sdist` through
`setup.py`.

The custom gRPC bdist command depends on numerous undocumented and
private behaviors of setuptools, wheel, distutils, etc. One such is the
ordering of generated distribution targets. We paper over this under the
assumption that the command will only be useful for gRPC devs, and
document with a command description a contractual obligation of users of
the command.

CONFIG != GRPC_CONFIG, meaning we're always building released, even in debug.

In order to output logs.