Cluster Autoscaler: unit tests not passing on 1.19 and 1.20

[towca]

The recent Azure cherry-picks to 1.19 and 1.20 (#4356, #4355) broke the Cluster Autoscaler build. It wasn't caught by CI because Github Actions hadn't been backported to 1.19 and 1.20. I tried fixing it, and there are 2 issues:

• Undefined FakeNodeReasonAnnotation and FakeNodeUnregistered. I think backporting annotate fakeNodes so that cloudprovider implementations can identify them #4119 should solve this.
• Undefined manager.RegisterNodeGroup. This method replaced manager.RegisterAsg in a large PR cleanup: refactor Azure cache and remove redundant API calls #3717. I tried replacing RegisterNodeGroup with RegisterAsg in the code manually, but the test that uses it still doesn't pass.

Github Actions are now running on 1.20 and 1.19.

Please fix ASAP.

@feiskyer @marwanad @nilo19

[marwanad]

Fixed in #4371 and #4370.

Sorry about that!

[towca]

Np, thanks for the quick fix!