[FEATURE REQUEST] Parallel test running option

[amgross]

Add utility of -jXX to run the unit tests (that anyway running in separate process) in parallel.

To avoid prints that will mix together, need that the processes won't write to stdout but will write to other place and just upon termination it will be copied to stdout. In case of no parallel, the output should go to stdout.

This change should be as light in runtime as can so it will really gain better time even for short tests.