HG-271: Fix test runner and add path-prefix support

Test runner was not running and falsely reporting success:
- [x] Add check for `Image` as it is not defined in node.js;
- [x] Add error message and exit code when the test runner fails;
- [x] Add `Vignette` namespace to the module; 
- [x] Add `path-prefix` support.
too much whitespace ^_^ `(function (testCase)`