Fix AttributeError while inserting a rule
Fix AttributeError while inserting a rule

When adding a rule with non-existent policy throws AttributeError
instead of raising an PolicyRuntimeException. This commit fixes the
same

Change-Id: I5a03e4869cda1fedbb253c6d033089b140e2fa14
Closes-Bug:#1497084

ekcs/congress,ekcs/congress,ekcs/congress,ramineni/my_congress,ramineni/my_congress,openstack/congress,ekcs/congress,ramineni/my_congress,openstack/congress,ramineni/my_congress