dom0-updates: launch console update in terminal emulator as "GUI"

GUI updaters and Packagekit are confused by networkless dom0 and often
report that:
 - cannot check for updates (because of no network connection)
 - no updates are available, even if they are

The latter happen mostly because PackageKit does not load dnf.conf, so
try to use /etc/yum.repos.d (network repositories) instead of
/etc/yum.real.repos.d (local cache, downloaded by qubes-dom0-update).
Currently PackageKit does not support configuring it, the path is
hardcoded.

Until both of above issues get fixed, prefer console updater.

Fixes QubesOS/qubes-issues#1378

dom0-updates/qubes-dom0-update

@@ -113,10 +113,10 @@ if [ "$GUI" == "1" -a -n "$PKGS" ]; then
 fi
 
 if [ "$GUI" == "1" ]; then
-    apps="yumex apper gpk-update-viewer"
+    apps="xterm konsole yumex apper gpk-update-viewer"
 
     if [ -n "$KDE_FULL_SESSION" ]; then
-        apps="apper yumex gpk-update-viewer"
+        apps="konsole xterm apper yumex gpk-update-viewer"
     fi
 
     guiapp=
@@ -125,6 +125,8 @@ if [ "$GUI" == "1" ]; then
             guiapp=$app
             case $guiapp in
                 apper) guiapp="apper --updates --nofork" ;;
+                xterm) guiapp="xterm -e sudo dnf update" ;;
+                konsole) guiapp="konsole --hold -e sudo dnf update" ;;
                 *) guiapp=$app ;;
             esac
             break;