raft: import etcd-io/raft at d9cb9933

[pav-kv]

This import contains minor test refactorings (the use of require/assert packages), and a flaky test fix.

git subtree pull --prefix pkg/raft [email protected]:etcd-io/raft.git d9cb9933

Epic: none Release note: none

[cockroach-teamcity]

This change is 

[pav-kv]

@nvanbenschoten PTAL. Testing the import flow with this PR.

[pav-kv]

bors r=nvanbenschoten

[craig[bot]]

Build failed:

• lint

[cockroach-teamcity]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 3 committers have signed the CLA.

:white_check_mark: pav-kv
:x: ahrtr
:x: MrDXY
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[nvb]

@pav-kv do we want to get this in?