core:If no power management configured or fails...

If no power management configured or fails to fence, alert user he must manually fence

Modify the code such that Alert is generated when a Restart operation is
requested by the Non Responding Treatment mechanism and skipped because
the Host lacks PM configuration.

Change-Id: I9e7affa4da23b4697f2677ad3d1c68befd1ff10f
Signed-off-by: Eli Mesika <emesika@redhat.com>