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Kube-dns configmap translation to CoreDNS

**What this PR does / why we need it**:
Translation of kube-dns ConfigMap (StubDomains and UpstreamNameserver) to equivalent Proxy in CoreDNS.

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes kubernetes/kubeadm#662

**Special notes for your reviewer**:

Currently, the translation is done as follows:
Example ConfigMap of kube-dns.
```
apiVersion: v1
data:
  federations: |
    {"foo" : "foo.feddomain.com"}
  stubDomains: |
    {"abc.com" : ["1.2.3.4"], "my.cluster.local" : ["2.3.4.5"]}
  upstreamNameservers: |
    ["8.8.8.8", "8.8.4.4"]
kind: ConfigMap
metadata:
  creationTimestamp: 2018-01-22T20:21:56Z
  name: kube-dns
  namespace: kube-system
```

CoreDNS Corefile after translation.

```
   .:53 {
        errors
        health
        kubernetes cluster.local  in-addr.arpa ip6.arpa {
           upstream  8.8.8.8 8.8.4.4
           pods insecure
           fallthrough in-addr.arpa ip6.arpa
        }
       federation cluster.local {
           foo foo.feddomain.com
        }
        prometheus :9153
        proxy .  8.8.8.8 8.8.4.4
        cache 30
    }
    abc.com:53 {
        errors
        cache 30
        proxy . 1.2.3.4
    }
    my.cluster.local:53 {
        errors
        cache 30
        proxy . 2.3.4.5
    }
```



**Release note**:

```release-note
Kubeadm: CoreDNS supports migration of the kube-dns configuration to CoreDNS configuration when upgrading the service discovery from kube-dns to CoreDNS as part of Beta. 
```