Merge pull request #3818 from poettering/exit-status-env

beef up /var/tmp and /tmp handling; set $SERVICE_RESULT/$EXIT_CODE/$EXIT_STATUS on ExecStop= and make sure root/nobody are always resolvable

diff --cc src/basic/fileio.c
Simple merge

diff --cc src/core/service.c
Simple merge

diff --cc src/core/socket.c
Simple merge