Formatter JUnit

The work on this Junit formatter at https://github.com/Behat/Behat/pull/527 seems to have stalled. I have take what was done by WouterJ done a refactor on the xml creation and completed the work. I have also brought the base inline with master so it can be merged.
this looks wrong to me. Having 2 different option printers and using one of them each time with lots of conditionals is not the right solution. you should have a different class containing the logic related to your ``suitePrinter``, and used for the junit formatting