title: Azure Deployment - Overide parameter with ARM functions
body: <p>I'm using VSTS to deploy azure resources.
  I use task "Azure Resource Group Deployment" to deploy ARM templates.
  How can I, for a specific parameter, override the value with a ARM function (concat, listkeys, etc)?</p>
  
  <p>Example: My ARM template has a parameter that is a storage account key and instead of providing the key directly, I want to provide it by passing [listkeys(...)]</p>