By default, docker containers inherit ulimit from limits of docker
deamon. On CentOS 7, docker daemon default NOFILE is 1048576.
It can found in /usr/lib/systemd/system/docker.service.
The big limit will cause many problem. we should control it in
production environment.

Change-Id: Iab962446a94ef092977728259d9818b86cfa7f68