MB-11287 Fix flusher,Conn notifier minSleepTime to save CPU

FlusherTask and connnotifyTask's minSleep time was set to 1.0s
With large number of buckets, this value gets averaged out to
sub-millisecond range causing all the threads to busy loop
Fix up their values to have exponential sleep upto MIN_SLEEP_TIME
for connotifyTask and 10seconds for flusher (we have a wake() method anyway)

Change-Id: Id557a38886e3af5fcce010a012c087f2e94ce337
Reviewed-on: http://review.couchbase.org/37928
Reviewed-by: Sundararaman Sridharan <sundar@couchbase.com>
Tested-by: Sundararaman Sridharan <sundar@couchbase.com>