weston-init: Error out if loading a nested instance

The Weston nested instance support is not implemented. This errors out
displaying an informative error message so someone insterested on it
may look at implement this later.

(From OE-Core rev: 2332f93ae88ca4e4a5aac1806f21104b6489b3bb)

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-graphics/wayland/weston-init/weston-start

@@ -14,6 +14,11 @@ if test $# -lt 2; then
 	exit 1
 fi
 
+if [ -n "$WAYLAND_DISPLAY" ]; then
+	echo "ERROR: A Wayland compositor is already running, nested Weston instance is not supported yet."
+	exit 1
+fi
+
 openvt_args=""
 while [ -n "$1" ]; do
 	openvt_args="$openvt_args $1"