livenet: don't attempt to download the image for every interface

https://bugzilla.redhat.com/show_bug.cgi?id=1152485
(cherry picked from commit e5f4bbd804)

modules.d/90livenet/livenetroot.sh

@@ -7,12 +7,20 @@ type getarg >/dev/null 2>&1 || . /lib/dracut-lib.sh
 
 PATH=/usr/sbin:/usr/bin:/sbin:/bin
 
+[ -e /tmp/livenet.downloaded ] && exit 0
+
 # args get passed from 40network/netroot
 netroot="$2"
 liveurl="${netroot#livenet:}"
 info "fetching $liveurl"
 imgfile=$(fetch_url "$liveurl")
-[ $? = 0 ] || die "failed to download live image: error $?"
+
+if [ $? = 0 ]; then
+	warn "failed to download live image: error $?"
+	exit 1
+fi
+
+> /tmp/livenet.downloaded
 
 # TODO: couldn't dmsquash-live-root handle this?
 if [ ${imgfile##*.} = "iso" ]; then