Start ScrubberTask when a memcache bucket is created
Start ScrubberTask when a memcache bucket is created

Previous code creates the ScrubberTask when default_engine
is loaded, creating a thread which may never be used and
can ony serve to confuse people and muddle support work.

Change-Id: Ieeaf5278a10521db3d767408f519388b3093124f
Reviewed-on: http://review.couchbase.org/56599
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>
Reviewed-by: Trond Norbye <60edd2ef23891a753f231b0c6f161dc634079a93@gmail.com>
Tested-by: buildbot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>

couchbase/memcached,daverigby/memcached,daverigby/memcached,couchbase/memcached,owendCB/memcached,couchbase/memcached,daverigby/memcached,daverigby/kv_engine,owendCB/memcached,couchbase/memcached,daverigby/memcached,daverigby/kv_engine,owendCB/memcached,daverigby/kv_engine,daverigby/kv_engine,owendCB/memcached