Add a wireguard example and test

This uses the new features

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

test/cases/000_build/100_examples/070_wireguard/test.sh

@@ -0,0 +1,23 @@
+#!/bin/sh
+# SUMMARY: Test the wireguard example
+# LABELS:
+
+set -e
+
+# Source libraries. Uncomment if needed/defined
+#. "${RT_LIB}"
+. "${RT_PROJECT_ROOT}/_lib/lib.sh"
+
+IMAGE_NAME=wireguard
+
+clean_up() {
+	# remove any files, containers, images etc
+	rm -rf ${IMAGE_NAME}*
+}
+
+trap clean_up EXIT
+
+# Test code goes here
+moby build "${LINUXKIT_EXAMPLES_DIR}/${IMAGE_NAME}.yml" 
+
+exit 0