Randomize pbjs global name when testing (prebid#1787)

* Fix test that hard-coded pbjs global.

* Randomize pbjs global name when testing.

Causes tests that hard-code global name to break.

karma.conf.maker.js

@@ -1,7 +1,7 @@
 // This configures Karma, describing how to run the tests and where to output code coverage reports.
 //
 // For more information, see http://karma-runner.github.io/1.0/config/configuration-file.html
-
+process.env.test = true;
 var _ = require('lodash');
 var webpackConf = require('./webpack.conf');
 var path = require('path')

webpack.conf.js

@@ -10,6 +10,8 @@ var neverBundle = [
   'AnalyticsAdapter.js'
 ];
 
+var prebidGlobalName = process.env.test ? 'pbjs_' + Math.floor(Math.random() * 10000) : prebid.globalVarName;
+
 module.exports = {
   devtool: 'source-map',
   resolve: {
@@ -77,7 +79,7 @@ module.exports = {
             {
               pattern: /\$\$PREBID_GLOBAL\$\$/g,
               replacement: function (match, p1, offset, string) {
-                return prebid.globalVarName;
+                return prebidGlobalName;
               }
             }
           ]