Merge pull request kubernetes#58828 from rajansandeep/configtranslate

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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. 
```

cmd/kubeadm/app/features/features.go

@@ -54,7 +54,7 @@ var InitFeatureGates = FeatureList{
 	StoreCertsInSecrets: {FeatureSpec: utilfeature.FeatureSpec{Default: false, PreRelease: utilfeature.Alpha}},
 	// We don't want to advertise this feature gate exists in v1.9 to avoid confusion as it is not yet working
 	HighAvailability:     {FeatureSpec: utilfeature.FeatureSpec{Default: false, PreRelease: utilfeature.Alpha}, MinimumVersion: v190, HiddenInHelpText: true},
-	CoreDNS:              {FeatureSpec: utilfeature.FeatureSpec{Default: false, PreRelease: utilfeature.Alpha}, MinimumVersion: v190},
+	CoreDNS:              {FeatureSpec: utilfeature.FeatureSpec{Default: false, PreRelease: utilfeature.Beta}, MinimumVersion: v190},
 	DynamicKubeletConfig: {FeatureSpec: utilfeature.FeatureSpec{Default: false, PreRelease: utilfeature.Alpha}, MinimumVersion: v190},
 	Auditing:             {FeatureSpec: utilfeature.FeatureSpec{Default: false, PreRelease: utilfeature.Alpha}},
 }

cmd/kubeadm/app/phases/addons/dns/BUILD

@@ -18,7 +18,9 @@ go_test(
         "//cmd/kubeadm/app/util:go_default_library",
         "//pkg/apis/core:go_default_library",
         "//pkg/util/version:go_default_library",
+        "//vendor/k8s.io/api/core/v1:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/api/errors:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/apis/meta/v1:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/runtime:go_default_library",
         "//vendor/k8s.io/client-go/kubernetes/fake:go_default_library",
         "//vendor/k8s.io/client-go/testing:go_default_library",
@@ -41,6 +43,7 @@ go_library(
         "//cmd/kubeadm/app/util/apiclient:go_default_library",
         "//pkg/api/legacyscheme:go_default_library",
         "//pkg/util/version:go_default_library",
+        "//vendor/github.com/mholt/caddy/caddyfile:go_default_library",
         "//vendor/k8s.io/api/apps/v1:go_default_library",
         "//vendor/k8s.io/api/core/v1:go_default_library",
         "//vendor/k8s.io/api/rbac/v1:go_default_library",