title: Get karaf env variables inside camelContext
body: <p>I am trying to get karaf env variables inside camelContext
  I have added</p>
  
  <p><code>&lt;ext:property-placeholder placeholder-prefix="$[" placeholder-suffix="]"/&gt;</code></p>
  
  <p>outside camelcontext and tried to use the karaf.home inside camelcontext. But its failing load the data from that location. I've tried like this </p>
  
  <p><code>
  &lt;camelContext id="_camelContext"
          xmlns="http://camel.apache.org/schema/blueprint"&gt;
  &lt;propertyPlaceholder id="config" location="file:$[karaf.home]/etc/application_config.prope‌​rties" /&gt;
  &lt;/camelContext&gt;</code></p>
  
  <p>Can't we access it inside camelcontext?</p>