core: Report unreachable domain names when setting host as non operational

When setting a host as non operation because an error reaching one or more
storage domains, the audit log will now report the names of
the unreachable storage domains

Signed-off-by: Tal Nisan <tnisan@redhat.com>
Bug-Url: https://bugzilla.redhat.com/1079583
Change-Id: I1dc385da76b6a4b0776d783c0df33fa737d206c0