Use stack variable instead of instance var to indicate retrying after authentication.
Otherwise an exception during authentication will wedge for future requests(self._retry_after_authn never reset to false).

Change-Id: I441836a400843f41da1c1adcc8700cdd79a85366
(cherry picked from commit 968c2388d3d196c30c0c609a5fb464eaac22e456)
Merge "Use stack variable instead of instance var to indicate retrying after authentication. Otherwise an exception during authentication will wedge for future requests(self._retry_after_authn never reset to false)."