[3.4] etcdserver,pkg: remove temp files in snap dir when etcdserver starting

[vivekpatani]

• Backporting: etcdserver: remove temp files in snap dir when etcdserver starting #12846
• Reference: Plans for v3.4.20 release #14232

Please read https://github.com/etcd-io/etcd/blob/main/CONTRIBUTING.md#contribution-flow.

[vivekpatani]

@ahrtr looks like I've missed a few things, I'll have it fixed in sometime.

[serathius]

I would be worried about making improvements/patches to cherry-picked commits. When cherry-picking we should do minimal changes to original code so it works with older branch.

We should not improve the code during cherry-pick. Back-porting should be focused on fixing bug and not alter the code from main branch. Back-port should also flow from newest release. If there are any places for improvements, please start from main and release-3.5 branches.

[ahrtr]

I would be worried about making improvements/patches to cherry-picked commits. When cherry-picking we should do minimal changes to original code so it works with older branch.

Actually there are already some changes on the main branch, and they are exactly what I pointed out. The defer os.RemoveAll(tmpdir) isn't correct, we should remove it. Other comments isn't a big deal, personally I would suggest to update it as well, but I will not insist on it.

[ahrtr]

Specifically, the PR 12846 is already out of date in the main branch.

[ahrtr]

LGTM

Thank you @vivekpatani

[ahrtr]

IT's a minor and accordingly safe change, merging...