Let ${surefire.forkNumber} deliver unique values when used in parallel mvn builds

Currently, ${surefire.forkNumber} is resolved to a unique value only for a single instance of the surefire execution. E.g. With forkCount=1, the place holder will always be resolved as 1, even if tests are being executed concurrently by multiple instances of surefire within a mvn -T... build.

I'll start creating a path within the next couple of days...