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

Fix for #48 with IT.
Updated documentation for runOrder parameter.
Added ststem property for runOrder.
please name the parameter "surefire.runOder" and "failsafe.runOrder" in the Surefire mojo and the IntegrationTest mojo. We already have a Jira-issue flying around that asks us to rename some existing properties, so we shouldn't introduce new ones without those prefixes.