Fix metadata labeler test flakes

[torredil]

What type of PR is this?

/kind cleanup

What is this PR about? / Why do we need it?

Update metadata labeler unit tests to be deterministic by removing instances of time.Sleep() and other anti-patterns in the testing code that make it brittle / prone to flakes. See testgrid: https://testgrid.k8s.io/provider-aws-ebs-csi-driver#ci-unit-test.

How was this change tested?

go test -race -v ./pkg/cloud/metadata -run "^Test(GetMetadata|PatchSingleNode|PatchNodes|VolumeIDIndexFunc|GetNonCSIManagedVolumes)$" -count=100 -timeout=10m

Does this PR introduce a user-facing change?

NONE

[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 torredil for approval. For more information see the 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

[github-actions]

Code Coverage Diff

File	Old Coverage	New Coverage	Delta
github.com/kubernetes-sigs/aws-ebs-csi-driver/pkg/cloud/metadata/labels.go	57.8%	49.1%	-8.7