Polish grpcio_health_checking package

-Rename namespace to grpc_health->grpc to match spec
-Proper use of NOT_FOUND status code
-Improve testing
-Add source distribution to artifact build
diff --git a/src/python/grpcio_tests/setup.py b/src/python/grpcio_tests/setup.py
index 7eef420..0afaf7d 100644
--- a/src/python/grpcio_tests/setup.py
+++ b/src/python/grpcio_tests/setup.py
@@ -75,7 +75,7 @@
     # Run `preprocess` *before* doing any packaging!
     'preprocess': commands.GatherProto,
 
-    'build_proto_modules': grpc.tools.command.BuildProtoModules,
+    'build_package_protos': grpc.tools.command.BuildPackageProtos,
     'build_py': commands.BuildPy,
     'run_interop': commands.RunInterop,
     'test_lite': commands.TestLite