Use proper log

When lrmd kills monitor process at the time of stop, following warning and error are output.

```
lrmd[4876]: warning: operation_finished: group1_prmApPostgreSQLDB406_monitor_10000:2861 - terminated with signal 9
lrmd[4876]: error: services_action_cancel: Termination of group1_prmApPostgreSQLDB406_monitor_10000 failed
```

In this case, __info__ level will be enough for the 'terminated with signal'.

It relates to https://github.com/ClusterLabs/pacemaker/pull/457.