cgroup driver is <empty> when execute pouch info

[zhangxiaoyu-zidif]

Ⅰ. Issue Description

when I execute pouch info, and check cgroup driver,
the value is empty.

Ⅱ. Describe what happened

see above.

Ⅲ. Describe what you expected to happen

it should show systemd or cgroupfs

Ⅳ. How to reproduce it (as minimally and precisely as possible)

1. pouch info 2>/dev/null | grep 'Cgroup Driver:' | grep -v "#" | awk -F: '{print $2}' | sed 's/ //g'

Ⅴ. Anything else we need to know?

None

Ⅵ. Environment:

• pouch version (use pouch version): 1.0.0-rc1

• OS (e.g. from /etc/os-release):

• Kernel (e.g. uname -a): Linux z05i10391.sqa.zth 3.10.0-327.ali2011.alios7.x86_64 add travis.yml for CI #1 SMP Tue Jun 6 14:29:12 CST 2017 x86_64 x86_64 x86_64 GNU/Linux

• Install tools:

• Others:

[xiaoxubeii]

Indeed, it doesn't return CgroupDriver in https://github.com/alibaba/pouch/blob/master/daemon/mgr/system.go#L118.