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/download/tasks/prep_kubeadm_images.yml

@@ -38,6 +38,7 @@
   shell: "set -o pipefail && {{ bin_dir }}/kubeadm config images list --config={{ kube_config_dir }}/kubeadm-images.yaml | grep -Ev 'coredns|pause'"
   args:
     executable: /bin/bash
+  environment: "{{ proxy_disable_env }}"
   register: kubeadm_images_raw
   run_once: true
   changed_when: false