Add OAuth interop tests to Python

Also adds the commands to the grpc_docker shell library script to
support running in docker.
diff --git a/src/python/interop/setup.py b/src/python/interop/setup.py
index 7a32992..502fcbe 100644
--- a/src/python/interop/setup.py
+++ b/src/python/interop/setup.py
@@ -45,7 +45,7 @@
         'credentials/server1.pem',]
 }
 
-_INSTALL_REQUIRES = ['grpcio>=0.4.0a4']
+_INSTALL_REQUIRES = ['oauth2client>=1.4.7', 'grpcio>=0.4.0a4']
 
 setuptools.setup(
     name='interop',