replication: improve join/subscribe logging

This patch makes logging a little bit more verbose so as to facilitate
post-mortem replication failure analysis:

 - When an instance starts up, print its uuid and vclock.
 - When a replica connects to a master, print the master's uuid to
   the replica's log.
 - Print replica uuid and address to the master's log on join/subscribe.
 - Log local and remote vclock on subscribe, both on master and on
   replica.
 - Log ids assigned to replicas both on recovery and when online.
   Also, log when a replica is deleted from the cluster.