Ensure to_dict() returns auth_tok

* ReddwarfContext was changed to defer to the parent's to_dict method.
  When the context is serialized to amqp, it is known by the key 'auth_token'
  instead of the expected 'auth_tok' as a side-effect.

fixes bug 1152827

Change-Id: I8fcdb2a3eaf8da0dda3c0229b24e32f528353619