CBQE-948 clean up the atop seriesly db when celery starts

Change-Id: I475a2c11b9e67c42ee3c81a343dfd66fbc7a0db4
Reviewed-on: http://review.couchbase.org/24172
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Chisheng Hong <chisheng@couchbase.com>