Use a variable for standardizing kubectl invocation (#8329)

* Add kubectl variable

* Replace kubectl usage by kubectl variable in roles

* Remove redundant --kubeconfig on kubectl usage

* Replace unecessary shell usage with command

roles/network_plugin/ovn4nfv/tasks/main.yml

@@ -0,0 +1,15 @@
+---
+- name: ovn4nfv | Label control-plane node
+  command: >-
+    {{ kubectl }} label --overwrite node {{ groups['kube_control_plane'] | first }} ovn4nfv-k8s-plugin=ovn-control-plane
+  when:
+    - inventory_hostname == groups['kube_control_plane'][0]
+
+- name: ovn4nfv | Create ovn4nfv-k8s manifests
+  template:
+    src: "{{ item.file }}.j2"
+    dest: "{{ kube_config_dir }}/{{ item.file }}"
+  with_items:
+    - {name: ovn-daemonset, file: ovn-daemonset.yml}
+    - {name: ovn4nfv-k8s-plugin, file: ovn4nfv-k8s-plugin.yml}
+  register: ovn4nfv_node_manifests