CCBC-530: Persist vbucket configuration heuristics across updates

Change-Id: I2b5d3390c8566fed705c2eaec5d421973bb68ec9
Reviewed-on: http://review.couchbase.org/42405
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>