Bug 1128141 - HostController gets DOWN when name attribute in host.xml is
empty

Fallback to detect host name using on $HOSTNAME and others in case we don't
find it in host.xml

(cherry picked from commit 9c2868cc0d54b3394edaf1ccea6f60c2ec959d69)
Signed-off-by: Libor Zoubek <lzoubek@redhat.com>