mgr/cephadm: catch CancelledError in asyncio timeout handler

mgr/cephadm: catch CancelledError in asyncio timeout handler

Specifically, concurrent.futures.CancelledError. At least on
python 3.9, this error can be raised when certain commands
being run asynchronously fail. Not catching this results in
the whole cephadm module crashing with something like

Traceback (most recent call last):
  File "/usr/share/ceph/mgr/cephadm/utils.py", line 94, in do_work
    return f(*arg)
  File "/usr/share/ceph/mgr/cephadm/serve.py", line 267, in refresh
    r = self._refresh_facts(host)
  File "/usr/share/ceph/mgr/cephadm/serve.py", line 370, in _refresh_facts
    val = self.mgr.wait_async(self._run_cephadm_json(
  File "/usr/share/ceph/mgr/cephadm/module.py", line 671, in wait_async
    return self.event_loop.get_result(coro, timeout)
  File "/usr/share/ceph/mgr/cephadm/ssh.py", line 64, in get_result
    return future.result(timeout)
  File "/lib64/python3.9/concurrent/futures/_base.py", line 444, in result
    raise CancelledError()
concurrent.futures._base.CancelledError

Fixes: https://tracker.ceph.com/issues/64473
Signed-off-by: Adam King <adking@redhat.com>