Add /usr/libexec/launch script to image

scripts/build-user-rootfs-stage-two

@@ -10,6 +10,16 @@ export LANG=en_US.UTF-8 LC_ALL=en_US.UTF-8 LC_CTYPE=en_US.UTF-8
 mkdir -p /etc/systemd/user.conf.d
 printf '[Manager]\nDefaultEnvironment="DISPLAY=:0"\n' > /etc/systemd/user.conf.d/50-display-env.conf
 
+mkdir -p /usr/libexec
+cat > /usr/libexec/launch <<- 'EOF'
+	#!/bin/bash
+	export DISPLAY=:0
+	export DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus
+	export XDG_RUNTIME_DIR=/run/user/1000
+	$@
+EOF
+chmod +x /usr/libexec/launch
+
 echo "subgraph" > /etc/hostname
 echo "deb http://http.debian.net/debian unstable main" >> /etc/apt/sources.list
 useradd -s /bin/bash -m user