Ensure kubeadm doesn't use proxy (#7275)

* Move proxy_env to kubespray-defaults/defaults

There is no reasons to use set_facts here

Signed-off-by: Etienne Champetier <e.champetier@ateme.com>

* Ensure kubeadm doesn't use proxy

*_proxy variables might be present in the environment (/etc/environment, bash profile, ...)
When this is the case we end up with those proxy configuration in /etc/kubernetes/manifests/kube-*.yaml manifests

We cannot unset env variables, but kubeadm is nice enough to ignore empty vars
93d288e2a4/cmd/kubeadm/app/util/env.go (L27)

Signed-off-by: Etienne Champetier <e.champetier@ateme.com>

roles/kubernetes/kubeadm/tasks/kubeadm_etcd_node.yml

@@ -22,6 +22,7 @@
     {{ kubeadm_discovery_address }}
   args:
     creates: "{{ kube_cert_dir }}/apiserver-etcd-client.key"
+  environment: "{{ proxy_disable_env }}"
 
 - name: Delete unneeded certificates
   file: