title: Orion CB Error in <updateAction> DELETE
body: <p>I need to delete an attribute of a entity but I obtain error "No context element found". I have applied the xml example of the tutorial (<a href="https://forge.fiware.org/plugins/mediawiki/wiki/fiware/index.php/Publish/Subscribe_Broker_-_Orion_Context_Broker_-_User_and_Programmers_Guide#Adding_and_removing_attributes_with_APPEND_and_DELETE_in_updateContext" rel="nofollow">Tutorial</a>). </p>
  
  <p>The attribute that I want to delete is 'timestamp'. I have checked that this exits. Here I show the output:</p>
  
  <pre><code>&lt;?xml version="1.0"?&gt;
  &lt;queryContextResponse&gt;
  &lt;contextResponseList&gt;
  &lt;contextElementResponse&gt;
    &lt;contextElement&gt;
      &lt;entityId type="Sensor" isPattern="false"&gt;
        &lt;id&gt;1&lt;/id&gt;
      &lt;/entityId&gt;
      &lt;contextAttributeList&gt;
        &lt;contextAttribute&gt;
          &lt;name&gt;timestamp&lt;/name&gt;
          &lt;type&gt;string&lt;/type&gt;
          &lt;contextValue&gt;2015-04-15 11:10:00&lt;/contextValue&gt;
        &lt;/contextAttribute&gt;
      &lt;/contextAttributeList&gt;
    &lt;/contextElement&gt;
    &lt;statusCode&gt;
      &lt;code&gt;200&lt;/code&gt;
      &lt;reasonPhrase&gt;OK&lt;/reasonPhrase&gt;
    &lt;/statusCode&gt;
  &lt;/contextElementResponse&gt;
  </code></pre>
  
  <p>
  </p>
  
  <p>And here the xml code to delete it:</p>
  
  <pre><code>(curl localhost:1026/NGSI10/updateContext -s -S --header 'Content-Type: application/xml' -d @- | xmllint --format - ) &lt;&lt;EOF
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;updateContextRequest&gt;
  &lt;contextElementList&gt;
  &lt;contextElement&gt;
    &lt;entityId type="Sensor" isPattern="false"&gt;
      &lt;id&gt;1&lt;/id&gt;
    &lt;/entityId&gt;
    &lt;contextAttributeList&gt;
      &lt;contextAttribute&gt;
        &lt;name&gt;timestamp&lt;/name&gt;
        &lt;type&gt;string&lt;/type&gt;
        &lt;contextValue/&gt;
      &lt;/contextAttribute&gt;
    &lt;/contextAttributeList&gt;
  &lt;/contextElement&gt;
  &lt;/contextElementList&gt;
  &lt;updateAction&gt;DELETE&lt;/updateAction&gt;
  &lt;/updateContextRequest&gt;
  EOF
  </code></pre>
  
  <p>Could you help me?</p>