Ensure that each server is tried during a config heartbeat

Change-Id: I7547effadbc5a76fb5c801450c0f069d2b272d32
Reviewed-on: http://review.couchbase.org/42426
Tested-by: Jeffry Morris <jeffrymorris@gmail.com>
Reviewed-by: Matt Ingenthron <matt@couchbase.com>