title: dotnet restore NuGet.Config environment variables for ClearTextPassword doesn't work
body: <p>To do CI I'd like to checkin a NuGet.Config file with my own nuget feed (an VSTS one). Like this:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;configuration&gt;
    &lt;packageSources&gt;
      &lt;add key="myfeed" value="https://xxx.pkgs.visualstudio.com/_packaging/myfeed/nuget/v3/index.json" /&gt;
    &lt;/packageSources&gt;
    &lt;packageSourceCredentials&gt;
      &lt;myfeed&gt;
          &lt;add key="ClearTextPassword" value="%PASSWD%" /&gt;
      &lt;/myfeed&gt;
    &lt;/packageSourceCredentials&gt;
  &lt;/configuration&gt;
  </code></pre>
  
  <p>Because I don't want to check in the password, I read you can use Environment Variables in this configuration. I tried it and it works in the PackageSources value. But it seems it doesn't work in the PackageSourceCredentials like shown above.
  Does someone has a solution for this?</p>