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/kubernetes-apps/network_plugin/kube-router/tasks/main.yml

@@ -12,7 +12,7 @@
   run_once: true
 
 - name: kube-router | Wait for kube-router pods to be ready
-  command: "{{ bin_dir }}/kubectl -n kube-system get pods -l k8s-app=kube-router -o jsonpath='{.items[?(@.status.containerStatuses[0].ready==false)].metadata.name}'"   # noqa 601 ignore-errors
+  command: "{{ kubectl }} -n kube-system get pods -l k8s-app=kube-router -o jsonpath='{.items[?(@.status.containerStatuses[0].ready==false)].metadata.name}'"   # noqa 601 ignore-errors
   register: pods_not_ready
   until: pods_not_ready.stdout.find("kube-router")==-1
   retries: 30