Migrate NewInformer to cache.ListerWatcher

[mborsz]

Migrate informer.NewInformer to cache.ListerWatcher to:

• provide compile-time validation of resources (e.g. typo in resource name will be detected in compilation time)
• make it testable:
  • previous code uses on RESTClient which isn't implemented by kubernetes' fake.NewSimpleClientset()
  • this code uses a standard way of creating informers which is properly handled by fake.NewSimpleClientset()

I still let informer.NewInformer exists as it has convenient addEventHandler call.

/assign @wojtek-t

[wojtek-t]

/lgtm
/approve

[k8s-ci-robot]

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This pull-request has been approved by: mborsz, wojtek-t

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[mborsz]

/retest