Previously just depended on 'postgres' which was OK until we switched to
using the Postgres provided repository for postgres packages, which
makes postgres be postgres 10. Haven't tested any of the infrastructure
for 10 and don't want to start right now.

prepare-olddebian : does not do package file excludes
prepare-database: does not do package file excludes or dump databases

These are for use on machines where we can no longer reinstate them by
quickly and easily installing a new VM from the network and then
layering the backup on top, usually because the OS is obsolete.

This seems to be used for machines with postgres. It was also updated
to put exclude and log files in the new locations.

debian-zfs doesn't exist in Ubuntu.

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.