Ensure all Reporters accept a callback function

This change ensures all reporters accept a callback function for a third parameter of their `run()` function, which is fired when the tests are done.

`browser`, `lcov`, `nested`, `tap` and `verbose` needed these parameters.

`default`, `junit`, etc already accepted a 3rd callback parameter.

The reason for this change is because of a separate change I'm also pull-requesting for `grunt-contrib-nodeunit`, which adds `reporter` and `reporterOutput` options to choose the reporter and an optional output file for the results.  Prior to this change, if the grunt config specified a reporter that didn't accept the 3rd callback parameter, grunt would hang waiting for a callback that never happens.