Ingress-GCE does not GC LB resources when ingress class changed and no other ingress on GCE exists

[freehan]

Repro steps:

1. Make sure there is no ingress exists in the cluster.
2. Create a test ingress with no ingress class annotation
3. Wait for ingress-gce controller to provision LB
4. Add a non-GCE ingress class on the test ingress
5. The LB resources will be leaked.

Root cause:

• Ingress-gce controller does not act on non-relevant ingresses. https://github.com/kubernetes/ingress-gce/blob/release-1.3/pkg/controller/controller.go#L127
• Ingress-gce controller only GC resources in the ingress sync loop.
  https://github.com/kubernetes/ingress-gce/blob/release-1.3/pkg/controller/controller.go#L287

[rramkumar1]

/help-wanted
/good-first-issue

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[agadelshin]

Hi! I'd like to take this.

[rramkumar1]

@pondohva Thanks, send us a PR whenever you are ready!

/assign @pondohva

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In response to this:

@pondohva Thanks, send us a PR whenever you are ready!

/assign @pondohva

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