MB-8214 replace wake() with snooze()

Calling IOManager::wake() method from running task is
unnecessary. This only causes redundant resorting of
already sorted futureQ of running thread.

Change-Id: Ife0afcd0dc7f977af314d40124e62237e3def6d6
Reviewed-on: http://review.couchbase.org/26720
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Jin Lim <jin@couchbase.com>