Add k8s externaldns and coredns addons switchers

Those parameters needed to control deployment of externaldns and
coredns addons.
Also allowed to control externaldns image version and
base support of externaldns provider switch.
Externaldns and coredns disabled by default in any model.

Change-Id: I05fb713b7e7c053a990f4f3811a4c2042d420b36
diff --git a/classes/cluster/virtual-mcp11-k8s-contrail/kubernetes/init.yml b/classes/cluster/virtual-mcp11-k8s-contrail/kubernetes/init.yml
index 8268e6d..18f1369 100644
--- a/classes/cluster/virtual-mcp11-k8s-contrail/kubernetes/init.yml
+++ b/classes/cluster/virtual-mcp11-k8s-contrail/kubernetes/init.yml
@@ -31,12 +31,16 @@
     kubernetes_netchecker_server_image: mirantis/k8s-netchecker-server:v1.1.0
     kubernetes_netchecker_agent_probeurls: "http://ipinfo.io"
     kubernetes_virtlet_image: mirantis/virtlet:v0.7.0
+    kubernetes_externaldns_image: mirantis/external-dns:latest
+    kubernetes_externaldns_provider: coredns
 
     # switches of addons
     kubernetes_helm_enabled: true
     kubernetes_netchecker_enabled: true
     kubernetes_calico_policy_enabled: false
     kubernetes_virtlet_enabled: false
+    kubernetes_coredns_enabled: false
+    kubernetes_externaldns_enabled: false
 
     # addresses and hostnames
     kubernetes_internal_api_address: 10.254.0.1