nfs-idmapd.service would report following error when stopped:
Starting NFSv4 ID-name mapping service...
rpc.idmapd[1198]: Setting log level to 0
Started NFSv4 ID-name mapping service.
rpc.idmapd[1198]: exiting on signal 15
Stopping NFSv4 ID-name mapping service...
nfs-idmapd.service: Main process exited, code=exited, status=1/FAILURE
nfs-idmapd.service: Failed with result 'exit-code'.
Stopped NFSv4 ID-name mapping service.
commit 93e8f092(idmapd: Add graceful exit and resource cleanup)
redirected SIGTERM, so when executing "systemctl stop nfs-idmapd", the
main() of idmapd would running to tail to return, while it returned 1
which considered as error by systemd.
So here just return 0 in main().
(cherry picked from commit 03a9b6b8ca77aa603d265289709eedf032278466)
