MachinePool always update vmssState

[mweibel]

What type of PR is this?
/kind bug

What this PR does / why we need it:
Updates ScaleSets service to always update the scope's vmss state with the latest data.
Previously, a long running operation would cause the vmssState to not be updated and delayed creation of AzureMachinePoolMachines until much later when that long running operation completed.
This change avoids this and updates the vmssState to what is retrieved from the API at all times.
The call does not make more API requests because the VMSS GET request was done anyway but its result ignored.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes kubernetes-sigs/cluster-api#9858 for CAPZ

Special notes for your reviewer:

Question: Should I add a test which tests this specific case with a long running operation? Is there any existing test which resembles this?

• cherry-pick candidate

TODOs:

• squashed commits
• includes documentation
• adds unit tests

Release note:

Improves state update handling when running long operations on VMSS

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please assign jackfrancis for approval. For more information see the Kubernetes Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[k8s-ci-robot]

Hi @mweibel. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[mweibel]

FYI this is a small refactoring I noticed while looking through the tests - ReconcileReplicas never returns an error and I adjusted its signature therefore.

[jackfrancis]

This change to the interface could be up for discussion, but it would have to ship with a minor release, we wouldn't be able to include this as a bug fix in a patch release. I assume we want to get this fix out, so I'd advise removing this change from this PR.

[willie-yao]

/ok-to-test

[willie-yao]

/lgtm
/assign @nojnhuh

[jackfrancis]

/lgtm cancel

I think we want to classify this as a bug fix so we can backport, in which case we'll want to remove the updates to internal interfaces.

[codecov]

Codecov Report

Attention: Patch coverage is 57.14286% with 12 lines in your changes missing coverage. Please review.

Project coverage is 52.57%. Comparing base (5b2cbce) to head (e3e9230).
Report is 12 commits behind head on main.

Files with missing lines	Patch %	Lines
azure/services/scalesets/scalesets.go	58.33%	6 Missing and 4 partials ⚠️
azure/scope/machinepool.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5292      +/-   ##
==========================================
- Coverage   52.57%   52.57%   -0.01%     
==========================================
  Files         272      272              
  Lines       29408    29414       +6     
==========================================
+ Hits        15460    15463       +3     
- Misses      13150    13151       +1     
- Partials      798      800       +2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

---

🚨 Try these New Features:

• Flaky Tests Detection - Detect and resolve failed and flaky tests