title: How to set value of variable group variable in TFS Build
body: <p>In <a href="https://stackoverflow.com/questions/57674793/azure-devops-how-to-set-the-value-of-the-variable-in-variable-group">this thread</a> the setting of a variable group variable in an Azure Devops build is discussed.
  My question is if there is also a way to set the value of a variable group variable by a TFS Build.
  To be concrete: I'd like to store the current value of the <code>$(Rev:r)</code> variable of a build pipeline in a variable group to use it in a different build pipeline.</p>