Add retry_stagger var for failed download/pushes.

* Add the retry_stagger var to tweak push and retry time strategies.
* Add large deployments related docs.

Signed-off-by: Bogdan Dobrelya <bdobrelia@mirantis.com>

roles/kubernetes/master/tasks/main.yml

@@ -12,7 +12,7 @@
   register: kube_task_result
   until: kube_task_result.rc == 0
   retries: 4
-  delay: "{{ 20 | random + 3 }}"
+  delay: "{{ retry_stagger | random + 3 }}"
   changed_when: false
 
 - name: Write kube-apiserver manifest