Provide time-based threshold for resetting configuration

This provides a time-based threshold so that low-use modes can get
configuration refreshes fairly quickly

Change-Id: If1de2d8b380a4823e95ddb0c608c842d5e19f7be
Reviewed-on: http://review.couchbase.org/32893
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>