title: Travis: how to know android sdk/ndk path?
body: <p>My android project is built with Ant and i have to edit <code>ant.properties</code> manually file to pass <code>sdk.path</code> variable pointing to android sdk directory. i'm going to change it to get sdk path from environment variable to make build possible on Travis CI. What is android sdk variable for this? </p>
  
  <p>Also i have some jni code to be built with android ndk, so the similar question - what is env variable for android ndk on Travis?</p>