rename map.py to diff.py, sort minions within a pool, ...

Making some changes suggested in initial commit for this runner described here:
https://github.com/saltstack/salt/pull/10684

* rename map.py to diff.py, (suggested by @holmboe)
* sort the minions within a pool,
* more clear output format,
* wrap comments at col. 80 (requested by @gtmanfred)