Re-replicator: bookie checking should handle flapping bookie registration

Problem:

currently re-replicator only uses the view of available/readonly bookies right at the time doing bookie checking. it would accidentally treat a bookie disappeared from zookeeper (e.g. zookeeper session expired, bookie restarted, flapping bookie registration due to network/gc) as lost bookies, which introduce unnecessary re-replication.

Solution:

introduce 'auditorStaleBookieInterval', if a bookie never register in the given interval, it would be marked as 'stale' bookies and re-replicate all ledgers belongs to that bookie. the default value is set 30 minutes.

Fixes:

• refactor bookie watcher to allow notifying bookie list thru BookiesListener
• introduce 'auditorStaleBookieInterval' to be able to mark bookies as 'stale' if bookies aren't registered themselves to zookeeper
• add more info logging about critical steps on re-replication logic
• misc changes