In order to standardize the way dbsync are run across our modules,
we create a new class designate::db::sync and
designate::db::powerdns::sync.
Those classes will be included if sync_db is enabled.
By making this transition the designate::db::sync class and the powerdns
related one can be returned by the ENC.
A use case would be in an highly available environment, with 3 galera
nodes, include designate::db on every node with sync_db set to false
and have the ENC return designate::db::sync just for one node.
Change-Id: I3e14b82055cfadf3274d6657413668b11f28ec49
3d4879dc4d