lrm: do not migrate if service already running upon rebalance on start

lrm: do not migrate if service already running upon rebalance on start

As reported in the community forum[0], currently, a newly added
service that's already running is shut down, offline migrated and
started again if rebalance selects a new node for it. This is
unexpected.

An improvement would be online migrating the service, but rebalance
is only supposed to happen for a stopped->start transition[1], so the
service should not being migrated at all.

The cleanest solution would be for the CRM to use the state 'started'
instead of 'request_start' for newly added services that are already
running, i.e. restore the behavior from before commit c2f2b9c
("manager: set new request_start state for services freshly added to
HA") for such services. But currently, there is no mechanism for the
CRM to check if the service is already running, because it could be on
a different node. For now, avoiding the migration has to be handled in
the LRM instead. If the CRM ever has access to the necessary
information in the future, to solution mentioned above can be
re-considered.

Note that the CRM log message relies on the fact that the LRM only
returns the IGNORED status in this case, but it's more user-friendly
than using a generic message like "migration ignored (check LRM
log)".

[0]: https://forum.proxmox.com/threads/125597/
[1]: https://pve.proxmox.com/pve-docs/chapter-ha-manager.html#_crs_scheduling_points

Suggested-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
 [ T: split out adding the test to a previous commit so that one can
   see in git what the original bad behavior was and how it's now ]
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>