vm/prepare-dvm: wait for Xorg in more deterministic way (#636)

vm-init.d/qubes_core_appvm

@@ -13,7 +13,7 @@ possibly_run_save_script()
 	echo $ENCODED_SCRIPT|perl -e 'use MIME::Base64 qw(decode_base64); local($/) = undef;print decode_base64(<STDIN>)' >/tmp/qubes_save_script
 	chmod 755 /tmp/qubes_save_script
 	Xorg -config /etc/X11/xorg-preload-apps.conf :0 &
-	sleep 2
+	while ! [ -S /tmp/.X11-unix/X0 ]; do sleep 0.5; done
 	DISPLAY=:0 su - user -c /tmp/qubes_save_script
 	killall Xorg
 }

vm-systemd/prepare-dvm.sh

@@ -7,7 +7,7 @@ possibly_run_save_script()
 	echo $ENCODED_SCRIPT|perl -e 'use MIME::Base64 qw(decode_base64); local($/) = undef;print decode_base64(<STDIN>)' >/tmp/qubes_save_script
 	chmod 755 /tmp/qubes_save_script
 	Xorg -config /etc/X11/xorg-preload-apps.conf :0 &
-	sleep 2
+	while ! [ -S /tmp/.X11-unix/X0 ]; do sleep 0.5; done
 	DISPLAY=:0 su - user -c /tmp/qubes_save_script
 	killall Xorg
 }