Refactor all gRPC proxy code into a single class.

appengine/swarming/swarming_bot/bot_code/remote_client.py

 # Copyright 2016 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
 
 import base64
 import logging
+import os
 import threading
 import time
 import traceback
 import urllib
 
 from utils import net
 
 from remote_client_errors import BotCodeError
 from remote_client_errors import InitializationError
 from remote_client_errors import InternalError
@@ skipping 18 matching lines @@
 AUTH_HEADERS_EXPIRATION_SEC = 4*60+30
 
 
 # How long to wait for a response from the server. Must not be greater than
 # AUTH_HEADERS_EXPIRATION_SEC, since otherwise there's a chance auth headers
 # will expire while we wait for connection.
 NET_CONNECTION_TIMEOUT_SEC = 3*60
 
 
 def createRemoteClient(server, auth, grpc_proxy):
+  grpc_proxy = os.environ.get('SWARMING_GRPC_PROXY', grpc_proxy)
   if grpc_proxy:
     import remote_client_grpc
     return remote_client_grpc.RemoteClientGrpc(grpc_proxy)
   return RemoteClientNative(server, auth)
 
 
 class RemoteClientNative(object):
   """RemoteClientNative knows how to make authenticated calls to the backend.
 
   It also holds in-memory cache of authentication headers and periodically
@@ skipping 258 matching lines @@
         'account_id': account_id,
         'id': bot_id,
         'scopes': scopes,
         'task_id': task_id,
     })
     if not resp:
       raise InternalError('Error when minting the token')
     if resp.get('error'):
       raise MintOAuthTokenError(resp['error'])
     return resp