auditing rebalance start

Change-Id: Ic3f66ee294eea0119d10b8322c2994c93144c13a
Reviewed-on: http://review.couchbase.org/43222
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>