Bug#760948: post-inst script fails while adding group systemd-journal if it exists

[pothos at riseup.net]

Thanks for reading so fast ;)

myuser at hostname:~$ sudo getent group systemd-journal
systemd-journal:x:1007:myuser

myuser at hostname:~$ sudo addgroup --system systemd-journal
addgroup: The group `systemd-journal' already exists and is not a system
group. Exiting.