Fix node public IP fetching from instance metadata service

[feiskyer]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespaces from that line:

/kind api-change
/kind bug
/kind cleanup
/kind design
/kind documentation
/kind failing-test
/kind feature
/kind flake
/kind bug

What this PR does / why we need it:

When VM or VMSS is bounded with "standard" LoadBalancer, the instance's public IP address would not be part of http://169.254.169.254/metadata/instance. Hence, kubectl get nodes would not show public IP address when using "standard" LoadBalancer.

This PR fixes the issue by fetching public IP from IMDS loadbalancer endpoint http://169.254.169.254/metadata/loadbalancer .

Which issue(s) this PR fixes:

Fixes #535

Special notes for your reviewer:

Release note:

Fix node public IP fetching from instance metadata service when the node is part of standard load balancer backend pool.

[k8s-ci-robot]

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[nilo19]

/lgtm