title: Define buildconfigfield for an specific flavor AND buildType
body: <p>I have 2 flavors, lets say Vanilla and Chocolate. I also have Debug and Release build types, and I need Vanilla Release to have a field true, while the other 3 combinations should be false.</p>
  
  <pre><code>def BOOLEAN = "boolean"
  def VARIABLE = "VARIABLE"
  def TRUE = "true"
  def FALSE = "false"
  
      VANILLA {
  
          debug {
  
              buildConfigField BOOLEAN, VARIABLE, FALSE
  
          }
  
          release {
  
              buildConfigField BOOLEAN, VARIABLE, TRUE
  
          }
  
  
      }
  
      CHOCOLATE {
          buildConfigField BOOLEAN, VARIABLE, FALSE
      }
  </code></pre>
  
  <p>I'm having an error, so I guess the debug and release trick doesnt work. It is possible to do this?</p>