CBQE-2270: fragmentation_monitor.cancel() if SetViewInfoNotFound

Change-Id: I2f576b81fb8c74a19a51a77b1b93a5a823ba49f2
Reviewed-on: http://review.couchbase.org/37901
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>