setting nodes for shutdown in scaleset shutdown

[anshuman-goel]

Summary of the Pull Request

I have observed that shutting down scaleset doesn't actually removes node. using similar strategy as in pools for it.

PR Checklist

• Applies to work item: Manage Scalesets within pool #124
• CLA signed. If not, go over here and sign the CLI.
• Tests added/passed
• Requires documentation to be updated
• I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: #xxx

Info on Pull Request

What does this include?

Validation Steps Performed

manually

[bmc-msft]

I understand the issue you're trying to address but I think aligning Scaleset.shutdown and Pool.shutdown is probably in order rather than this PR.

I'll work on that tomorrow.

[bmc-msft]

In the short term, going forward with this PR. We can address cleaning up pool/scaleset/node shutdown cleanup in a later effort.

[bmc-msft]

Performing integration tests