minor improvements to CLI of likwid-mpirun

[davydden]

would be good to add the following to likwid-mpirun CLI:

1. support of --stats to make output the same regardless of one core and multiple cores
2. support automatic filtering via --output file.json

this makes post-processing data easier.

[TomTheBear]

Other feature requests concerning likwid-mpirun:

1. Support for the colon syntax: mpirun -n 1 ./a.out : -n 1 ./a.out
2. Fix problems if "--" on cmdline but not meant for likwid-mpirun: likwid-mpirun -np 2 wrapper_app -opt x -- real_app