Use .zuulrc credentials for Sauce Labs tests

See #605 (comment)

bin/test.js

@@ -1,8 +1,15 @@
 #!/usr/bin/env node
 
 var spawn = require('cross-spawn-async')
+var findNearestFile = require('find-nearest-file')
+var path = require('path')
+var userHome = require('user-home')
+var pathExists = require('path-exists')
 
-var runSauceLabs = process.env.SAUCE_USERNAME && process.env.SAUCE_ACCESS_KEY
+// .zuulrc logic from https://github.com/defunctzombie/zuul/blob/a0de46a5906c84b19f655c487f7c8debe938984d/bin/zuul#L384
+var zuulrcPath = findNearestFile('.zuulrc') || path.join(userHome, '.zuulrc')
+var hasSauceLabEnvVars = process.env.SAUCE_USERNAME && process.env.SAUCE_ACCESS_KEY
+var runSauceLabs = hasSauceLabEnvVars || pathExists.sync(zuulrcPath)
 
 npmRun('test-node', function (code) {
   if (code === 0) {

package.json

@@ -83,12 +83,15 @@
     "cross-spawn-async": "^2.0.0",
     "electron-prebuilt": "^0.36.7",
     "finalhandler": "^0.4.0",
+    "find-nearest-file": "^1.0.0",
+    "path-exists": "^2.1.0",
     "run-series": "^1.0.2",
     "serve-static": "^1.9.3",
     "simple-get": "^2.0.0",
     "standard": "^6.0.1",
     "tape": "^4.0.0",
     "uglify-js": "^2.4.15",
+    "user-home": "^2.0.0",
     "zuul": "^3.0.0"
   },
   "homepage": "https://webtorrent.io",