Low: stonithd: Decrease log level of monitor

This changes Log Level of a __monitor__ of stonith resources to DEBUG, because that of monitor which lrmd performs is DEBUG. I think that log level of __monitor__ of lrmd and stonithd should be unified.

Log level of the following messages will be set to DEBUG by this commit.
```
stonith-ng[22732]:     info: stonith_action_create: Initiating action monitor for agent fence_legacy (target=(null))
stonith-ng[22732]:     info: log_operation: F7:22809 [ Performing: stonith -t external/ipmi -S ]
stonith-ng[22732]:     info: log_operation: F7:22809 [ success:  0 ]
stonith-ng[22732]:     info: stonith_command: Processed st_execute from lrmd.22733: Operation now in progress (-115)
```