Make `bin/load_acls`'s device grouping algorithm read from a configurable parameter in `settings.py`

[jathanism]

The current grouping algorithm is hard-coded to a pattern match on the hostname of the device. That is why I did factor it out to the group() function as you determined, so that we can make this something that can be tweaked in the settings.

Let's move this criteria to a callable that can be found within settings.py.