MB-100: add logging for rebalancer thread

Change-Id: Ie4a686d2270de7434a8cb56c2434e96495ab2f6f
Reviewed-on: http://review.couchbase.org/23883
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>
Tested-by: Pavel Paulau <pavel.paulau@gmail.com>
CBQE-969: RH object has no attribute wait_for_repl

wait_for_replication from rest_client is deprecated ( when we wait node.replication = 1.0)
it have to be replaced on RebalanceHelper.wait_for_replication as Chiyoung suggested

Change-Id: Ibab375112be07a48653dd3cbc798b214232bf729
Reviewed-on: http://review.couchbase.org/23841
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>