pmacct - also create group for systemuser

after Ib674b02ce64f8a0 it now uses the default
puppet type instead of generic::systemuser,
which means we also need to create the group

currently on rhenium:

id pmacct
uid=997(pmacct) gid=1001(pmacct) groups=1001(pmacct),1002(systemusers)

Change-Id: I0533a4da4ddf06d10fb7dcec96588190839f4576
Merge "pmacct - also create group for systemuser" into production