title: how to build different variants of android through gradle
body: <p>I already have</p>
  <blockquote>
  <p>2 flavours (staging, production)</p>
  <p>2 buildTypes (debug, release)</p>
  </blockquote>
  <p>beyond that, I want to have different variants for, say, different vendors.
  like a production-release build for samsung and htc. is it possible through build scripts?</p>
  <p>PS: I don't want to use 3rd party plugin like <a href="https://github.com/ihrthk/android-gradle-mulchannel-plugin" rel="nofollow noreferrer">this</a></p>