Currently to run borg job manually, you have to use systemctl:
```
$ systemctl start borgbackup-job-jobname.service
```
This commit makes wrappers around borg jobs available in $PATH, which have
BORG_REPO and connection args set correctly:
```
$ borg-job-jobname list
$ borg-job-jobname mount ::jobname-archive-2019-12-25T00:01:29 /mnt/some-path
$ borg-job-jobname create ::test /some/path
```
Closes: https://github.com/NixOS/nixpkgs/pull/64888
Co-authored-by: Danylo Hlynskyi <abcz2.uprola@gmail.com>
When having backup jobs that persist to a removable device like an
external HDD, the directory shouldn't be created by an activation script
as this might confuse auto-mounting tools such as udiskie(8).
In this case the job will simply fail, with the former approach
udiskie ran into some issues as the path `/run/media/ma27/backup` was
already there and owned by root.