e2e: Consolidate opt-in/opt-out handling to prevent flakes

[RamLavi]

What this PR does / why we need it:
tests sometimes fail when switching from opt-in to opt-out because it takes time for the k8s API to eventually consist the new labels behavior.
In some places there is an ugly sleep wait.
Instead, add optInNamespaceForVMs() and optOutNamespaceForVMs() wrappers that perform the opt-mode change, wait for webhook configuration propagation using Eventually().
Replace sleep() calls throughout tests.

Special notes for your reviewer:

Release note:

NONE

[qinqon]

/lgtm
/approve

[kubevirt-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: qinqon

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[RamLavi]

/cherry-pick release-0.49
/cherry-pick release-0.47

[kubevirt-bot]

@RamLavi: #576 failed to apply on top of branch "release-0.47":

Applying: Consolidate opt-in/opt-out handling to prevent flakes
Using index info to reconstruct a base tree...
M	tests/tests.go
M	tests/virtual_machines_test.go
Falling back to patching base and 3-way merge...
Auto-merging tests/virtual_machines_test.go
CONFLICT (content): Merge conflict in tests/virtual_machines_test.go
Auto-merging tests/tests.go
CONFLICT (content): Merge conflict in tests/tests.go
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config advice.mergeConflict false"
Patch failed at 0001 Consolidate opt-in/opt-out handling to prevent flakes

Details

In response to this:

/cherry-pick release-0.49
/cherry-pick release-0.47

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.

[RamLavi]

/cherry-pick release-0.49

[kubevirt-bot]

@RamLavi: #576 failed to apply on top of branch "release-0.49":

Applying: Consolidate opt-in/opt-out handling to prevent flakes
Using index info to reconstruct a base tree...
M	tests/tests.go
M	tests/virtual_machines_test.go
Falling back to patching base and 3-way merge...
Auto-merging tests/virtual_machines_test.go
CONFLICT (content): Merge conflict in tests/virtual_machines_test.go
Auto-merging tests/tests.go
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config advice.mergeConflict false"
Patch failed at 0001 Consolidate opt-in/opt-out handling to prevent flakes

Details

In response to this:

/cherry-pick release-0.49

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.