title: Pass through a variable to an included playbook
body: <p>I am including another playbook from my playbook. I need to pass it a variable, called <code>required_node_version</code>. I am using the same variable in my playbook, so was expecting that the included playbook will inherit it. But it doesn't causing 'undefined' error. So I tried to use this not very elegant solution:</p>
  
  <pre><code>- hosts: localhost
    connection: local
    vars:
      required_node_version: v6.3.1
  
    ...    
  
  - include: ../../base/ci/build.yml
    vars:
      required_node_version: "{{required_node_version}}"
  </code></pre>
  
  <p>Which causes <code>{"failed": true, "msg": "ERROR! recursive loop detected in template string: {{required_node_version}}"}</code>.</p>
  
  <p>Any elegant solution for this?</p>