add: LOCAL_BINARY_PATH variable to the config

User can use the already present local binary on their file system for
setting up the local tunnel on their system. As a fallback it will use
the legacy path so that the build doesn't break for already running
users.

Author: Yash Ladha

README.md

@@ -320,6 +320,7 @@ To avoid duplication of system or user specific information across several confi
 * `BROWSERSTACK_KEY`: BrowserStack key.
 * `TUNNEL_ID`: Identifier for the current instance of the tunnel process. In `TRAVIS` setup `TRAVIS_JOB_ID` will be the default identifier.
 * `BROWSERSTACK_JSON`: Path to the browserstack.json file. If null, `browserstack.json` in the root directory will be used.
+* `BROWSERSTACK_LOCAL_BINARY_PATH`: Path to the browserstack local binary present on the system. If null, `BrowserStackLocal` in the `lib/` directory will be used.
 
 
 ### Secure Information
@@ -348,10 +349,10 @@ To run a larger suite of tests ensuring compatibility with older versions of QUn
 Tests are also run for every pull request, courtesy [Travis CI](https://travis-ci.org/).
 
 ### Timeout issue with Travis CI
- 
-You might face [build timeout issue on Travis](https://docs.travis-ci.com/user/common-build-problems/#Build-times-out-because-no-output-was-received) if runner takes more than 10 minutes to run tests. 
 
-There are 2 possible ways to solve this problem: 
+You might face [build timeout issue on Travis](https://docs.travis-ci.com/user/common-build-problems/#Build-times-out-because-no-output-was-received) if runner takes more than 10 minutes to run tests.
+
+There are 2 possible ways to solve this problem:
   1. Run a script which does `console.log` every 1-2 minutes. This will output to console and hence avoid Travis build timeout
   2. Use `travis_wait` function provided by Travis-CI. You can prefix `browserstack-runner` command by `travis-wait` in your `travis.yml` file
 

bin/cli.js

@@ -421,11 +421,11 @@ function runTests(config, callback) {
   }
 }
 
-exports.run = function(user_config, callback) {
+exports.run = function(userConfig, callback) {
   callback = callback || function() {};
 
   try {
-    config = new (require('../lib/config').config)(user_config);
+    config = new (require('../lib/config').config)(userConfig);
 
     client = BrowserStack.createClient({
       username: config.username,

lib/local.js

@@ -11,6 +11,8 @@ var Log = require('./logger'),
 var Tunnel = function Tunnel(key, port, uniqueIdentifier, config, callback) {
   var that = {};
 
+  localBinary = process.env.BROWSERSTACK_LOCAL_BINARY_PATH || localBinary;
+
   function tunnelLauncher() {
     var tunnelOptions = getTunnelOptions(key, uniqueIdentifier);