This is patch #2 of 3 to rename the term bay to cluster within
the internal references and objects of magnum. This patch changes
all references to the certificate objects bay_uuid field to
cluster_uuid. Certifcate does not have a db table so no db
changes were made. No functionality is changed by this patch,
just internal naming.
Change-Id: I68a3b87b75b49de43a7855355807b50a4ae695f3
Implements: blueprint rename-bay-to-cluster