Add busted unit testing framework for lua code

rootfs/etc/nginx/lua/test/balancer_test.lua

@@ -0,0 +1,3 @@
+describe("[balancer_test]", function()
+  -- TODO: write tests 
+end)

rootfs/etc/nginx/lua/test/up.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+
+# Copyright 2018 The Kubernetes Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+if luarocks list --porcelain busted $BUSTED_VERSION | grep -q "installed"; then
+  echo busted already installed, skipping ;
+else
+  echo busted not found, installing via luarocks...;
+  sudo luarocks install busted $BUSTED_VERSION;
+fi