fix: change labels and service name from kube-dns to coredns

[idanlevin]

What this PR does / why we need it:
This PR fixes the coredns labels and service name
Which issue this PR fixes :
Fixes #199

Special notes for your reviewer:

If applicable:

• documentation
• unit tests
• tested backward compatibility (ie. deploy with previous version, upgrade with this branch)

Release note:

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[tariq1890]

Can you rebase this PR @idanlevin ?

[tariq1890]

Thanks for your contribution @idanlevin :). These changes certainly make sense, I had a look at the coredns repo and the deployment YAMLs over there still use the k8s-app: kube-dns as the label.

See here

It might be worthwhile to clarify the reasoning behind this label usage with the coredns maintainers. Thoughts?

[idanlevin]

@tariq1890 yes, I also see it's kept this way in the Kubernetes repo, I'll try to get a hold of the maintainers.

[idanlevin]

posted the question here -
coredns/deployment#116

will update

[mboersma]

@idanlevin the goimports error in the CircleCI tests was fixed by #205. Sorry about that! Could you rebase this PR off the master branch? It should pass tests after that.

[idanlevin]

I'm closing this PR since it seems to be by design as described here:
coredns/deployment#116