cli: make ceph tell mon.* version work

Fixes: #6767
Signed-off-by: Mykola Golub <mgolub@mirantis.com>
qa: refactor 'ceph -w' magic in test_mon_misc by introducing helper
functions ceph_watch_start and ceph_watch_wait so they can be reused
in other tests.

Signed-off-by: Mykola Golub <mgolub@mirantis.com>
qa: add test_tell, which currently is used only for testing 'ceph tell mon version'.

Signed-off-by: Mykola Golub <mgolub@mirantis.com>