Run dlt-daemon under the '_dlt' user instead of 'nobody'
See: https://bugs.debian.org/1055580
Fix is based on dlt-daemon 2.18.10-9:
- dlt-daemon depends on adduser
- Add dlt-daemon.postinst and dlt-daemon.postrm from 2.18.10-9 to handle creation and deletion of the "_dlt" user and group.