Fixes #7498 - CoreOS Getting Started Guide had invalid cloud config

Fixed node.yml and master.yml to work in environments where eth1
does not exist.

Also included an explicit setting for etcdctl in the flannel config

docs/getting-started-guides/coreos/cloud-configs/master.yaml

@@ -12,7 +12,6 @@ coreos:
     etcd-servers: http://localhost:4001
     metadata: "role=master"
   flannel:
-    interface: eth1
   units:
     - name: setup-network-environment.service
       command: start

docs/getting-started-guides/coreos/cloud-configs/node.yaml

@@ -5,7 +5,6 @@ coreos:
     etcd-servers: http://<master-private-ip>:4001
     metadata: "role=node"
   flannel:
-    interface: eth1
     etcd_endpoints: http://<master-private-ip>:4001
   units:
     - name: etcd.service
@@ -18,6 +17,7 @@ coreos:
         - name: 50-network-config.conf
           content: |
             [Service]
+            Environment=ETCDCTL_PEERS=http://<master-private-ip>:4001
             ExecStartPre=/bin/bash -c "until curl http://<master-private-ip>:4001/v2/machines; do sleep 2; done"
             ExecStartPre=/usr/bin/etcdctl set /coreos.com/network/config '{"Network":"10.244.0.0/16", "Backend": {"Type": "vxlan"}}'
     - name: docker.service