When calculating session_time, use the actual token life

This calculation uses the 'token_life' var which is a
datetime.timedelta object.  timedelta.seconds gets us just the
'seconds' component of the object, truncating away any days, hours,
or weeks that might be included in the object.

What we want here is the total time in seconds, which is
total_seconds().

Closes-Bug: #1562452
Change-Id: I6a947abb891e1d34e1cf3aea53b345e0a804bacf

openstack_auth/backend.py

@@ -263,7 +263,7 @@ class KeystoneBackend(object):
             request.user = user
             timeout = getattr(settings, "SESSION_TIMEOUT", 3600)
             token_life = user.token.expires - datetime.datetime.now(pytz.utc)
-            session_time = min(timeout, token_life.seconds)
+            session_time = min(timeout, int(token_life.total_seconds()))
             request.session.set_expiry(session_time)
 
             scoped_client = keystone_client_class(session=session,