MB-100: cancel timeout when it is not necessary anymore

Change-Id: I7439aa2e425d55048bf9f2eef885681fcc094d8e
Reviewed-on: http://review.couchbase.org/19770
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>
Tested-by: Pavel Paulau <pavel.paulau@gmail.com>