Added --trace-warnings to tests

- We've been getting warnings in our tests for some time now, but without --trace-warnings they are impossible to trackdown
- Add this flag for all tests so that we can see stack traces and maybe fix some of the issues

Gruntfile.js

@@ -133,6 +133,7 @@ const configureGrunt = function (grunt) {
                 reporter: grunt.option('reporter') || 'spec',
                 timeout: '60000',
                 require: ['core/server/overrides'],
+                flags: ['--trace-warnings'],
                 exit: true
             },