[release/1.6] fix: support simultaneous create diff for same parent snapshot

[vvoland]

Cherry-pick into 1.6:

• fix: support simultaneous create diff for same parent snapshot #7204

This makes it possible to run rootfs.CreateDiff multiple times simultaneously.

Original PR message:
"""
In CreateDiff function, we wil create view snapshot base on parent snapshot,
view snapshot name is "<parent snapshot KEY>-parent-view",

so while, It does not support concurrent operations，other user will be return to the error that the snapshot already exists.

So, we add uniquePart() as a suffix.
"""

(cherry picked from commit 344431c)
Signed-off-by: Paweł Gronowski pawel.gronowski@docker.com

[k8s-ci-robot]

Hi @vvoland. Thanks for your PR.

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