Integrate with updated Travis CI build environment

- Use android-wait-for-emulator script shipped in Travis VM image
- Require build-tools-19.0.3 component, which is no longer preinstalled
- Specify all the required SDK components even if they are present on
  the Travis VM image. See travis-ci/travis-ci#2296
- Tweak a bit .travis.yml organization

See also https://github.com/travis-ci/docs-travis-ci-com/pull/91