core: we are fencing a host when putting it in...

core: we are fencing a host when putting it in maintenance after failed
reinstall

Enabling moving a Host to maintainance from non-operational status

Change-Id: Id4e2dd45352867ccf67bc7f824570f855f77e2f1
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=906389
Signed-off-by: Eli Mesika <emesika@redhat.com>