mgr/cephadm: rewrite/simplify describe_service

mgr/cephadm: rewrite/simplify describe_service

The prior implementation first tried to fabricate services based on the
running daemons, and then filled in defined services on top.  This led
to duplication and a range of small errors.

Instead, flip this around: start with the services that are defined,
and only fill in 'unmanaged' services where we need to.

Drop the osd kludges and instead rely on DaemonDescription.service_id to
return the right thing.

Signed-off-by: Sage Weil <sage@newdream.net>