'Assignment' has no attr 'get_domain_by_name'
'Assignment' has no attr 'get_domain_by_name'

The domain API has moved to the resource manager. While there are
redirects at the manager level so that most calls won't notice,
keystone-manage mapping_purge is making a direct driver call (bypassing
the manager). It needs to be updated to point to the resource manager
rather than the assignment manager.

Change-Id: Ia4fc89a0496bf9dc45300dbbe4cb776210340de4
Closes-Bug: 1427379

nuxeh/keystone,promptworks/keystone,mahak/keystone,jamielennox/keystone,jumpstarter-io/keystone,jumpstarter-io/keystone,jonnary/keystone,nuxeh/keystone,cernops/keystone,rushiagr/keystone,openstack/keystone,roopali8/keystone,rajalokan/keystone,vivekdhayaal/keystone,maestro-hybrid-cloud/keystone,dstanek/keystone,vivekdhayaal/keystone,jonnary/keystone,ilay09/keystone,mahak/keystone,himanshu-setia/keystone,rajalokan/keystone,dstanek/keystone,mahak/keystone,idjaw/keystone,rajalokan/keystone,ajayaa/keystone,dstanek/keystone,promptworks/keystone,openstack/keystone,jamielennox/keystone,maestro-hybrid-cloud/keystone,vivekdhayaal/keystone,takeshineshiro/keystone,dims/keystone,klmitch/keystone,cernops/keystone,ilay09/keystone,rushiagr/keystone,ajayaa/keystone,nuxeh/keystone,klmitch/keystone,roopali8/keystone,jumpstarter-io/keystone,ilay09/keystone,idjaw/keystone,himanshu-setia/keystone,promptworks/keystone,dims/keystone,takeshineshiro/keystone,rushiagr/keystone,openstack/keystone