title: can't get liquibase executeCommand changeset to do anything
body: <p>From the <a href="http://www.liquibase.org/documentation/changes/execute_command.html" rel="nofollow">liquibase docs</a>, it looks like an <code>executeCommand</code> changeset should just shell out and execute the given command (e.g., <code>mysqldump</code>).  But if I specify some changeset like</p>
  
  <pre><code>&lt;changeSet author="me" id="test"&gt;
      &lt;executeCommand executable="date" /&gt;
  &lt;/changeSet&gt;
  </code></pre>
  
  <p>then all I get is this error message</p>
  
  <pre><code>2016-07-20 10:02:43,675 ERROR [main] liquibase
  </code></pre>
  
  <p>even though the changeset gets marked as <code>EXECUTED</code> in the db.</p>
  
  <p>Even if I specify some different executable like a tiny test shell script, it doesn't look like it actually gets executed.</p>
  
  <p>Is there anything else that I need to specify in the changeset, or do I have some incorrect expectation about how an <code>executeCommand</code> changeset should work?</p>