title: Buildbot master.cfg conditional depending on property
body: <p>I face a weird problem with extremly slow file upload on my windows slave buildbot.
  For example a file upload of a 60Mb files takes almost 2 minutes whereas the same zip on the same network is only taking a few seconds.</p>
  
  <p>To work around this, I thought about using a good old scp to upload my files under Windows, but I didn't succeed there since I am not able to do a conditional choice of what function to use to upload the file given a property I previously set.</p>
  
  <p>I am trying to do so like this</p>
  
  <pre><code>if(Interpolate("%(prop:osName)s")=='windows'):
      uploadWindows(args)
  else:
      upload_file(args)
  </code></pre>
  
  <p>But I have no success doing that even if the osName property is correctly set.</p>