systemd: refactor and add latest commands (#6250)

* Order systemctl commands alphabetically

Simplifying the plugin maintenance.

Signed-off-by: Petr Šabata <contyk@redhat.com>

* Include the latest systemctl commands

Based on systemd-233.  I'm still keeping the old, now unsupported
commands for backwards compatibility as well.

Signed-off-by: Petr Šabata <contyk@redhat.com>

* Add daemon-reload (#3701)

Closes #3701
Co-authored-by: Javier Tia <javier.tia@gmail.com>