MB-9065 reset autofailover count after successful rebalance

Change-Id: I37629437827777786330a8e340c1d3aaf0a673c3
Reviewed-on: http://review.couchbase.org/32944
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>