How to load a offline image

[kedy-zhao]

Ⅰ. Issue Description

when use pouch load command to load a docker offline image, the log shows no error,
and then use "pouch images" command to list the images, there is nothing to show.

Ⅱ. Describe what happened

  the docker offline image can not load to pouch

Ⅲ. Describe what you expected to happen

    when use pouch load -i xxx.tar to load offline image,it should be shown for "pouch images"
   command

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

1. install pouch-1.3.0-1.el7.x86_64.rpm on centos 7.6
2. systemctl restart pouch && systemctl restart pouch-lxcfs
   3.pouch load -i nginx.tar

Ⅴ. Anything else we need to know?

Ⅵ. Environment:

• pouch version (use pouch version): 1.3.0
• OS (e.g. from /etc/os-release): centos 7.6.1810
• Kernel (e.g. uname -a):3.10.0-957
• Install tools:
• Others:

[pouchrobot]

Thanks for your contribution. 🍻 @kedy-zhao
While we thought ISSUE TITLE could be more specific, longer than 20 chars.
Please edit issue title instead of opening a new one.
More details, please refer to https://github.com/alibaba/pouch/blob/master/CONTRIBUTING.md

[ZYecho]

same with #2931 , we keep an open issue to relate it.