MB-11232 Wake up tasks in pendingQueue as well

TaskQueue::wake() routine was missing to look at the
tasks blocked in the pendingQueue causing the
ExecutorPool::unregister() routine to hang occasionally.

Change-Id: I3592a820ae7ef0d1c587a459f0f34ab6731bbdde
Reviewed-on: http://review.couchbase.org/37688
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>