(Back)port of PAXEXAM-926 (RMI port range is not configurable for forked container) towards the v4.x branch

[glimmerveen]

I've prepared a (back)port of an enhancement that was previously merged towards master (PAXEXAM-926). This enhancement is about being able to configure the RMI port (range) of a forked container.

This is particular useful features when running tests in parallel through surefire/failsafe's fork feature:

<configuration>
    <systemPropertyVariables>
        <pax.exam.forked.invoker.port.range.lowerbound>1${surefire.forkNumber}000</pax.exam.forked.invoker.port.range.lowerbound>
        <pax.exam.forked.invoker.port.range.upperbound>1${surefire.forkNumber}009</pax.exam.forked.invoker.port.range.upperbound>
    </systemPropertyVariables>
    <forkCount>2</forkCount>
</configuration>

Without this enhancement, the parallel execution of the tests in most cases fail due to multiple tests trying to claim the same RMI port at the same time.

The original commits used (by cherrie-picking):

• a6270b9 by @nfalco79 which was the initial commit of this feature (PAXEXAM-926)
• 2b4a85e by @rmannibucau which contained some improvements related to the unit tests of this feature.