sysusers: many different errnos to express one condition

sysusers: many different errnos to express one condition

See https://bugzilla.redhat.com/show_bug.cgi?id=1807768. It turns
out that sysusers cannot query if the group exists:
Failed to check if group dnsmasq already exists: No such process
...
Failed to check if group systemd-timesync already exists: No such process

When the same command is executed later, the issue does not occur. Not sure why
the behaviour in the initial transaction is different. But let's accept all
errors that the man pages list. We check if the user/group exists before creating
anyway, so this seems pretty safe.