mgr/cephadm: execute conf update when rotating secret

mgr/cephadm: execute conf update when rotating secret

This is a fixup for: mgr/cephadm: add daemon 'rotate-key' action

The way we rotate mgr's secret require:

1) writing the new pending-key to mgr's file,
2) restarting the mgr via the `mgr fail` mon command.

Unfortunately, we might be doing the first step wrongly.
`_create_daemoan()` is a coroutine (Python's `async def`)
while we don't `wait` for it. IIUC the underlying doc
correctly, this has no effect, and thus the mgr is restarted
with old key.

  "Note that simply calling a coroutine will not schedule
  it to be executed"

See: https://docs.python.org/3/library/asyncio-task.html#id1

Signed-off-by: Radoslaw Zarzynski <rzarzyns@redhat.com>