CBQE-1872 delete extra self in sleep function

Change-Id: Iddb6e56fd835f0b905a87d70f1386e2bf92581e7
Reviewed-on: http://review.couchbase.org/32464
Tested-by: Thuan Nguyen <soccon@gmail.com>
Reviewed-by: Ashvinder Singh <ashvindersingh@gmail.com>
Reviewed-by: Thuan Nguyen <soccon@gmail.com>