tests: TEST_crush_reject_empty must not run a mon

tests: TEST_crush_reject_empty must not run a mon

* Back in Hammer, the osd-crush.sh individual tests did not run the
  monitor, it was taken care of by the run() function. An attempt to run
  another mon fails with:

  error: IO lock testdir/osd-crush/a/store.db/LOCK: Resource temporarily
  unavailable

  This problem was introduced by cc1cc033930e8690a57674e842a003f6bbc7a242
  from https://github.com/ceph/ceph/pull/4936
* replace test/mon/mon-test-helpers.sh with test/ceph-helpers.sh as
  we need run_osd() in this newly added test
* update the run-dir of commands: ceph-helpers.sh use the different
  convention for the run-dir of daemons.

http://tracker.ceph.com/issues/11975 Refs: #11975

Signed-off-by: Loic Dachary <ldachary@redhat.com>