save snapshot from gc when unpack image

[yanxuean]

Signed-off-by: yanxuean yan.xuean@zte.com.cn

[yanxuean]

There is a window before the content.Config refers the top snapshot where the snapshots created by image.Unpack() are GCed.
When the user independently call image.Unpack() after calling Pull(), the image.Unpack() don't create context with lease by self, the user don't also. so it is not ok.
It is ok when calling Pull() with option WithPullUnpack , because we create lease in Pull().

Now it will be happened in cri-containerd, because we call Pull() without option WithPullUnpack first, and then call image.Unpack.
@dmcgowan @Random-Liu

[codecov-io]

Codecov Report

Merging #1802 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1802   +/-   ##
=======================================
  Coverage   49.35%   49.35%           
=======================================
  Files          77       77           
  Lines        7695     7695           
=======================================
  Hits         3798     3798           
  Misses       3253     3253           
  Partials      644      644

Flag	Coverage Δ
#linux	49.42% <ø> (ø)	⬆️
#windows	44.91% <ø> (ø)	⬆️

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[yanxuean]

/assign @dmcgowan @crosbymichael
PTAL

[Random-Liu]

@yanxuean Thanks a lot!
This really looks like the root cause! Thanks for looking into this!
If this works, this will make our test pretty green!
I'll take a look at this during the weekend. Thanks!

/cc @dmcgowan

[dmcgowan]

LGTM

[estesp]

LGTM

[crosbymichael]

@yanxuean does this fix #1785 ?

[yanxuean]

@crosbymichael Seem like there are another problem yet.