Currently our textcollector can sometimes fail with 'Failed to
create/acquire the lock /home/backup/$server/lock.exclusive (timeout)."
Instead of checking on a borg lock file, check if our backup snapshot
dir exists which the backup script creates and removes. This should give
less false positives then our current method.

Add a new role called prometheus_exporters which should be run on every
machine we have and starts different collectors depending on what group
the machine is in. Currently supported our the gitlab runner exporter,
rebuilder textcollector, mysqld-exporter, borg textcollector and an
node/arch exporter. The arch exporter monitors the security status and
pacman out of date packages gauge.