Fix list_mappings deprecation warning message
Fix list_mappings deprecation warning message

Without this patch, the identity:list_mappings policy uses the
deprecated name and check string for the old identity:get_mapping rule,
which means the resulting OR'd policy is wrong and the deprecation
message is confusing. Use the right one.

Change-Id: I3fc1cff61df6d64ea1fc98f54f98aba0cd35145c

mahak/keystone,openstack/keystone,openstack/keystone,mahak/keystone,mahak/keystone,openstack/keystone