Split logs for tasks with same target machine but different target filesystems into
different logfiles for easier debugging.

prepare-nondebian script creates a fake excludes file for the machine now if
one doesn't exist, because I keep forgetting to do it myself for Redhat
machines and then the zfs-rsync script fails.

Add missing log directory /var/log/chem-zfs-backups
Add missing dep on rsync
Add fakeroot to Makefile to allow non-root building

Forcing arcfour causes us not to be able to back up jessie machines.