title: Ansible: how to construct a variable from another variable and then fetch it's value
body: <p>Here is my problem I need to use one variable 'target_host' and then append '_host' to it's value to get another variable name whose value I need. 
  If you look at my playbook. Task nbr 1,2,3 fetch the value of variable however nbr 4 is not able to do what I expect. Is there any other way to achieve the same in ansible?</p>
  
  <pre><code>   ---
      - name: "Play to for dynamic groups"
        hosts: local 
        vars:
          - target_host: smtp
          - smtp_host: smtp.max.com
        tasks:
          - name: testing
            debug: msg={{ target_host }}
          - name: testing
            debug: msg={{ smtp_host }}
          - name: testing
            debug: msg={{ target_host }}_host
          - name: testing
            debug: msg={{ {{ target_host }}_host }}
  
  
  Output:
  
  TASK: [testing] *************************************************************** 
  ok: [127.0.0.1] =&gt; {
      "msg": "smtp"
  }
  
  TASK: [testing] *************************************************************** 
  ok: [127.0.0.1] =&gt; {
      "msg": "smtp.max.com"
  }
  
  TASK: [testing] *************************************************************** 
  ok: [127.0.0.1] =&gt; {
      "msg": "smtp_host"
  }
  
  TASK: [testing] *************************************************************** 
  ok: [127.0.0.1] =&gt; {
      "msg": "{{{{target_host}}_host}}"
  }
  </code></pre>