Feature #11766: rbd-mirror: basic structure
Interlock RBD mirroring daemon and acquiring exclusive lock
If a local librbd client attempts to acquire the exclusive lock when the previous epoch was owned by a different cluster, this event must be interlocked with the mirroring daemon. If the daemon can register a new epoch in all known peers (prepare, commit/revert), it will be safe to continue the current mirroring period. If there is a conflict with a peer (a remote thinks it already owns that epoch), a new period should be started.