Allow per-context rule in error messages
Allow per-context rule in error messages

For some multi-policy APIs we need to be able to vary the rule name
mentioned in the HTTP failure message. This makes common_policy_check()
honor callables for rule_name to resolve what we expect based on the
context being used.

Change-Id: I128b0ccd63eb98e5199ef1e8268346811057830f

openstack/nova,openstack/nova,mahak/nova,openstack/nova,mahak/nova,mahak/nova