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/calico/tasks/pre.yml

@@ -19,7 +19,7 @@
 
 - name: Calico | Get kubelet hostname
   shell: >-
-    set -o pipefail && {{ bin_dir }}/kubectl get node -o custom-columns='NAME:.metadata.name,INTERNAL-IP:.status.addresses[?(@.type=="InternalIP")].address'
+    set -o pipefail && {{ kubectl }} get node -o custom-columns='NAME:.metadata.name,INTERNAL-IP:.status.addresses[?(@.type=="InternalIP")].address'
     | egrep "{{ ansible_all_ipv4_addresses | join('$|') }}$" | cut -d" " -f1
   args:
     executable: /bin/bash