[SUREFIRE-1098] Fix runOrder=balanced is not working

Fix for #48 with IT.
Updated documentation for runOrder parameter.
Added ststem property for runOrder.
Any reason on limiting the visibility of those methods? There is code out there that builds upon Surefire and I wonder if we might break stuff for them - which would be OK if we have our reasons... :wink:

Same goes for createForkStarter and createInprocessStarter...