Zeppelin should default to trusted proxy for service definition

Currently the following section is in Zeppelin service definition

  <policies>
    <policy role="webappsec"/>
    <policy role="authentication" name="Anonymous"/>
    <policy role="rewrite"/>
    <policy role="authorization"/>
  </policies>

With the above, Zeppelin must authenticate the user. We should have Knox authenticate and not have the authentication type hardcoded into the service definition.