Fix a bug in admission-controller while using an external kubeconfig

[shafeeqes]

Which component this PR applies to?

admission-controller

What type of PR is this?

/kind bug

What this PR does / why we need it:

The kubeClient is built with the config which already takes care of both out-of-cluster and in-cluster cases, in

autoscaler/vertical-pod-autoscaler/common/kubeconfig.go

Lines 26 to 41 in 561a9da

	func CreateKubeConfigOrDie(kubeconfig string, kubeApiQps float32, kubeApiBurst int) *rest.Config {
	var config *rest.Config
	var err error
	if len(kubeconfig) > 0 {
	klog.V(1).Infof("Using kubeconfig file: %s", kubeconfig)
	// use the current context in kubeconfig
	config, err = clientcmd.BuildConfigFromFlags("", kubeconfig)
	if err != nil {
	klog.Fatalf("Failed to build kubeconfig from file: %v", err)
	}
	} else {
	config, err = rest.InClusterConfig()
	if err != nil {
	klog.Fatalf("Failed to create config: %v", err)
	}
	}

However, this client

autoscaler/vertical-pod-autoscaler/pkg/admission-controller/main.go

Line 126 in 561a9da

clientset := getClient()

which always uses InClusterConfig, is used for registering the webhook.

This PR replaces the usage of this client with the already built kubeClient.

Which issue(s) this PR fixes:

Fixes #4844

Special notes for your reviewer:

With #3769, out-of-cluster operation of VPA was enabled. However, this bug doesn't allow the admission-controller to startup.

Does this PR introduce a user-facing change?

A bug in the admission-controller while using out-of-cluster kubeconfig, is now fixed.

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[shafeeqes]

/cc @JensErat @bskiba

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[jbartosik]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jbartosik, rfranzke, shafeeqes

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• vertical-pod-autoscaler/OWNERS [jbartosik]

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