demo: use runc for buildah

Github crypto-perf/opae-nlb-demo image builds using buildah started
failing without a reason. While we could continue to debug the root
cause, let's admit the version is so old and a reasonable configuration
exists that makes the error go away: using BUILDAH_RUNTIME=runc just
like we use for the plugin images seems sufficient.

Signed-off-by: Mikko Ylinen <mikko.ylinen@intel.com>

Author: mythi

demo/build-image.sh

@@ -20,7 +20,7 @@ TAG=${TAG:-devel}
 if [ -z "$BUILDER" -o "$BUILDER" = 'docker' -o "$BUILDER" = 'podman' ] ; then
     ${BUILDER} build --pull -t ${IMG}:${TAG} "$CWD/$DIR/"
 elif [ "$BUILDER" = 'buildah' ] ; then
-    buildah bud  --pull-always -t ${IMG}:${TAG} "$CWD/$DIR/"
+    BUILDAH_RUNTIME=runc buildah bud --pull-always -t ${IMG}:${TAG} "$CWD/$DIR/"
 else
     (>&2 echo "Unknown builder $BUILDER")
     exit 1