title: Using msbuild I want to update a config file with values from teamcity
body: <p>I have some XML that looks something like this:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;XmlConfig instancetype="XmlConfig, Processing, Version=1.0.0.0, Culture=neutral"&gt;
    &lt;item&gt;
      &lt;key&gt;IsTestEnvironment&lt;/key&gt;
      &lt;value&gt;True&lt;/value&gt;
      &lt;encrypted&gt;False&lt;/encrypted&gt;
    &lt;/item&gt;
    &lt;item&gt;
      &lt;key&gt;HlrFtpPutDir&lt;/key&gt;
      &lt;value&gt;C:\DevPath1&lt;/value&gt;
      &lt;encrypted&gt;False&lt;/encrypted&gt;
    &lt;/item&gt;
    &lt;item&gt;
      &lt;key&gt;HlrFtpPutCopyDir&lt;/key&gt;
      &lt;value&gt;C:\DevPath2&lt;/value&gt;
      &lt;encrypted&gt;False&lt;/encrypted&gt;
    &lt;/item&gt;
  
     ....
  
  &lt;/Provisioning.Lib.Processing.XmlConfig&gt;
  </code></pre>
  
  <p>In TeamCity I have many system properties:</p>
  
  <pre><code> system.HlrFtpPutDir     H:\ReleasePath1
   system.HlrFtpPutCopyDir H:\ReleasePath2
  </code></pre>
  
  <p>What sort of MsBuild magic can I use to push these values into my XML file? In all there are 20 or so items.</p>