tests: mon id is incorrectly skipped

The argument is shifted and $1 should be used to get the mon id instead
of $2.

http://tracker.ceph.com/issues/9836 Fixes: #9836

Signed-off-by: Loic Dachary <loic-201408@dachary.org>
Merge pull request #2759 from dachary/wip-9836-test-mon-id

tests: mon id is incorrectly skipped