Fix leaking goroutine in multiple integration tests by migrating to common StartTestServer utility

[wojtek-t]

Ref #108483

Note to reviewer: I recommend reviewing commit by commit - apart from the first one they are all independent.

NONE

/kind cleanup
/priority important-longterm
/sig testing

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[aojea]

/assign

[aojea]

you always create the namespace after create the clients in this commit

watchPVC, err := testClient.CoreV1().PersistentVolumeClaims(namespaceName).Watch(context.TODO(), metav1.ListOptions{})

I think that doesn't matter, but is there any special reason?

[wojtek-t]

Before this PR we effectively weren't creating the namespace (CreateTestingNamespace isn't effectively creating a namespace:
https://github.com/kubernetes/kubernetes/blob/master/test/integration/framework/util.go#L54

So we didn't need the client for that.

After switching to more realistic apiserver in this PR (that e.g. has namespace admission plugins enabled) we have to actually create a namespace (or alternatively disable namespace admission plugins, but I think it's better to those test be as realistic as possible), which requires having a client.

So I need to do that after creating a client.

Now the options are:

• refactor the code by splitting client creation and setting up those watches (and create namespaces in the middle)
• leave as is and create namespace after calling createClients

Since this doesn't matter really, I chose a cheaper to execute option :)

[aojea]

one question #110229 (comment) only

[wojtek-t]

@aojea - thanks, responded - PTAL

[aojea]

/lgtm