mgr/cephadm: extend stray service detection with a general ignore hook

mgr/cephadm: extend stray service detection with a general ignore hook

Extend the system's current stray service detection with a new method on
the service classes so that new classes can hook into the stray services
in the case that ceph services and cephadm services have differing names
or use subsystems that call into ceph with different names (my use
case).

Signed-off-by: John Mulligan <phlogistonjohn@asynchrono.us>