'Release registration if it is held by the domain specified.
If the specified domain is registered for this domain then free it,
if it is not then do nothing - no exception is raised.
:param domain_id: the domain in question
:param type: type of registration, if None then all registrations
for this domain will be freed'

@abc.abstractmethod
def release_registration(self, domain_id, type=None):

    raise exception.NotImplemented()
