CBQE-0 add command to delete 7 days old log
that eats up all disk space in slave

Change-Id: Id63c03868eb388c0372e7db54d6212fc141717d4
Reviewed-on: http://review.couchbase.org/41591
Reviewed-by: Tommie McAfee <tommie@couchbase.com>
Tested-by: Thuan Nguyen <soccon@gmail.com>