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

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

Block Host from being re-installed if it is in the non-operational
state.

Change-Id: Ib4b5fa23de6db22bf075712b256b8652a692df0e
Signed-off-by: Eli Mesika <emesika@redhat.com>
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=906389