[bug] pouch pull doesn't support multi snapshotter now

[ZYecho]

Ⅰ. Issue Description

Ⅱ. Describe what happened

pouch pull cli has some issues when enable multi-snapshotter feature.

Ⅲ. Describe what you expected to happen

follows the reproduce step below, we should call unpack func when change pouch's snapshotter
even if the image have been pulled before using another sanpshotter.

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

1. pull an image a in snapshotter A
2. then change to another snapshotter B
3. pull image a again when using snapshotter B, then it will output image has been pulled before and didn't call containerd's unpack func.

Ⅴ. Anything else we need to know?

None

Ⅵ. Environment:

No need.