Make onos-gui bazel build hermetic

Change-Id: I24abb9c1a54314fb0dd00f40936e57f11280ebce
diff --git a/tools/gui/BUILD b/tools/gui/BUILD
index 49f18fc..0073e2c 100644
--- a/tools/gui/BUILD
+++ b/tools/gui/BUILD
@@ -1,6 +1,15 @@
-exports_files(
-    [
+filegroup(
+    name = "_tools-gui-gulp-files",
+    srcs = [
         "package.json",
         "gulpfile.babel.js",
-    ],
+    ] + glob(["gulp-tasks/**"]),
+)
+
+genrule(
+    name = "tools-gui-gulp",
+    srcs = [":_tools-gui-gulp-files"],
+    outs = ["tools-gui-gulp.tar"],
+    cmd = "cd tools/gui && tar cf ../../$@ .",
+    visibility = ["//visibility:public"],
 )