Tools: Add python script to run one simulation several times

multiRun.py - run an exported cooja simulation several times

Cooja can export a complete simulation setup to a jar file. This can be executed independently from the contiki / cooja environment. This python script allows to execute one simulation file several times with different seeds. This is useful for example for montecarlo evaluations of a simulation setup.

I introduced this tool at contiki-developers and got a lot of feedback. I think this tools would be useful for anyone who needs to execute a cooja simulation several times.
In order to avoid overusing disk space, this could be delayed until the thread is going to be executed in the 'executeCommand' function. The difference is that, when running for example 1000 repetitions with 10 threads; the current implementation will copy 1000 times the *.jar file in each "run_X" folder. By delaying the creation of the *.jar file only a *.jar file will exist per each running thread and will be deleted when that specific simulation is finished.