test/bdev: Call rbd_cleanup() only if rbd test was run

This is to avoid spammy stderr comming from ceph/stop.sh:

  + umount /dev/loop200p2
  umount: /dev/loop200p2: not mounted.
  + losetup -d /dev/loop200
  losetup: /dev/loop200: detach failed: No such device or address

Change-Id: Id1ecfc5da1a530c63d454bfacc8fb36c29549f8e
Signed-off-by: Michal Berger <michalx.berger@intel.com>
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/1006


Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Paul Luse <paul.e.luse@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Reviewed-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>