... (rhbz#2104141)
In the first version, I wanted to use POSIX quotes with $''. But that required
'printf %q', which brings in a dependency on coreutils.
Following mcr0mmand's suggestion, ${foo@Q} is used instead, which should work
equivalently, and does not require anything new.
Tested with 'sysusers.generate-pre.sh /usr/lib/sysusers.d/*conf'. The output is
the same before and after, apart from the dovecot user with a quote.
This tweaks the sysusers.d handling logic so that 'm' entries are
now translated to a series of groupadd + useradd + usermod call.
The last usermod call is the notable change, effectively affecting
the list of secondary groups now.
