Add 'mint_oauth_token' method to RPC client.

appengine/swarming/swarming_bot/bot_code/remote_client_errors.py

Index: appengine/swarming/swarming_bot/bot_code/remote_client_errors.py
diff --git a/appengine/swarming/swarming_bot/bot_code/remote_client_errors.py b/appengine/swarming/swarming_bot/bot_code/remote_client_errors.py
index 4dc6944d2a3760ea2f3d28fbe1d60c20e5c2bf4d..f62d62870389a74e00b0758f1736b3b2afb0c9e4 100644
--- a/appengine/swarming/swarming_bot/bot_code/remote_client_errors.py
+++ b/appengine/swarming/swarming_bot/bot_code/remote_client_errors.py
@@ -23,4 +23,8 @@ class InternalError(Exception):
 
 
 class PollError(Exception):
-  """Raised on unrecoverable errors when in RemoteClient.poll."""
+  """Raised on unrecoverable errors in RemoteClient.poll."""
+
+
+class MintOAuthTokenError(Exception):

[Vadim Sh., 2017/06/29 04:58:44]

I'm just following established pattern in the code... New method, new
exception...

[dnj, 2017/06/29 16:29:26]

Acknowledged.

+  """Raised on unrecoverable errors in RemoteClient.mint_oauth_token."""