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

[pothos at riseup.net]

Package: systemd
Version: 215-2
Severity: grave

After installation systemd.postinst fails with code 1 when the group
systemd-journal already exists because then addgroup returns code 1 even
with --quiet.
To resolve this I added || true in line 98 so that the script continues:

addgroup --quiet --system systemd-journal || true