core: Change misleading audit log message.

SYSTEM_CHANGE_STORAGE_POOL_STATUS_NO_HOST_FOR_SPM is called when
An spm is non responsive and and fencing it fails.

Changing text to: "Fencing failed on Storage Pool Manager ${VdsName}
for Data Center ${StoragePoolName}. Setting status to Non-Operational."

Change-Id: Ib3653ed1ac9dae8779c2abfe788d4aafaa48ed28
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=954301
Signed-off-by: Mooli Tayer <mtayer@redhat.com>