Replaces peach with parallel

This practically doubles the speed.

`echo bunka` on 666 nodes:
1:57.69 with peach
1:06.74 with parallel

`md5sum /etc/debian_version ; sleep 2` on 57 nodes:
29.817 with peach
14.595 with parallel
Merge pull request #3 from openminds/feature/parallel

Replaces peach with parallel