Export compile directory to guests

Use 9p over virtio to share files on the host with the guest domains.
The files are accessible in the guests /hostfs directory.

testing/scripts/build-rootimage

@@ -48,6 +48,7 @@ do_on_exit umount $LOOPDIR/proc
 mkdir -p $LOOPDIR/root/compile
 log_action "Mounting $ROOTIMGCOMPILEDIR as /root/compile"
 execute "mount -o bind $ROOTIMGCOMPILEDIR $LOOPDIR/root/compile"
+do_on_exit rm -r $LOOPDIR/root/compile
 do_on_exit umount $LOOPDIR/root/compile
 
 echo "Installing software from source"
@@ -63,3 +64,5 @@ done
 
 log_action "Removing /etc/resolv.conf"
 execute "rm -f $LOOPDIR/etc/resolv.conf"
+
+mkdir -p $LOOPDIR/hostfs