chore: add run-lerna script to run lerna with repo root

The script sets `LERNA_ROOT_PATH` to the root directory of loopback-next
monorepo and run `lerna` commands.

Author: raymondfeng

bin/run-lerna.js

@@ -0,0 +1,31 @@
+#!/usr/bin/env node
+// Copyright IBM Corp. 2017,2018. All Rights Reserved.
+// Node module: @loopback/cli
+// This file is licensed under the MIT License.
+// License text available at https://opensource.org/licenses/MIT
+
+/**
+ * This is an internal script to run `lerna` command with enviornment variable
+ * `LERNA_ROOT_PATH` set to the root directory of `loopback-next` monorepo
+ */
+'use strict';
+
+const path = require('path');
+const lerna = require('lerna');
+const build = require('../packages/build');
+
+function run(argv, options) {
+  const ls = new lerna.LsCommand(
+    null,
+    {json: true, loglevel: 'silent'},
+    path.join(__dirname, '..'),
+  );
+  const rootPath = ls.repository.rootPath;
+
+  process.env.LERNA_ROOT_PATH = rootPath;
+  const args = argv.slice(2);
+  return build.runCLI('lerna/bin/lerna', args, options);
+}
+
+module.exports = run;
+if (require.main === module) run(process.argv);