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/commands.py b/src/python/grpcio_tests/commands.py
index 171829b..5ee551c 100644
--- a/src/python/grpcio_tests/commands.py
+++ b/src/python/grpcio_tests/commands.py
@@ -138,7 +138,7 @@
 
   def run(self):
     try:
-      self.run_command('build_proto_modules')
+      self.run_command('build_package_protos')
     except CommandError as error:
       sys.stderr.write('warning: %s\n' % error.message)
     build_py.build_py.run(self)