[#70] Update k8s gates to use kubectl

Gates previously used airshipctl kubectl version, but the kubectl
subcommand is being removed.

Change-Id: Ie2caf03da3f49346eef95bb6d5d61df43a6a82eb

playbooks/airship-airshipctl-functional-existing-k8s.yaml

@@ -34,6 +34,6 @@
       - name: "airshipctl kubectl version"
         shell: |
           set -ex
-          airshipctl kubectl version
+          kubectl version
         args:
           chdir: "{{ zuul.project.src_dir }}"

roles/airshipctl-deploy-ephemeral-node/tasks/main.yaml

@@ -16,9 +16,9 @@
 
 - name: check airshipctl kubectl version
   command: >-
-    timeout 20 airshipctl \
+    timeout 20 kubectl \
     --kubeconfig {{ airshipctl_config_dir_default | default(ansible_env.HOME) }}/.airship/kubeconfig \
-    kubectl version
+    version
   register: airship_kubecofig_version
   retries: 50
   delay: 20