Use attribute instead of passing parameter
Use attribute instead of passing parameter

Start using self.user_creds_id attribute instead of passing it as
parameter in the fucntion _try_get_user_creds.

Change-Id: I5a0bd3a1d6734cccce4c15c9b34ef3aeb89a577d

cwolferh/heat-scratch,jasondunsmore/heat,cwolferh/heat-scratch,gonzolino/heat,noironetworks/heat,openstack/heat,steveb/heat,gonzolino/heat,jasondunsmore/heat,dims/heat,noironetworks/heat,dragorosson/heat,openstack/heat,dragorosson/heat,dims/heat,steveb/heat