examples: simplistic async_polling.yml

examples/playbook/async_polling.yml

+---
+
+- hosts: all
+  gather_facts: false
+  tasks:
+
+  - name: simulate long running op (15 sec), wait for up to 45 sec, poll every 5 sec
+    command: /bin/sleep 10
+    async: 15
+    poll: 1