Add Android CI support

Even some minimal testing would probably be useful.

Servo has this running with the following:
https://github.com/servo/servo/blob/master/etc/run_in_headless_android_emulator.py
https://github.com/servo/servo/blob/9a0404ac5fc1c463aa68bb0c68d709a61157c2bf/etc/ci/buildbot_steps.yml#L175-L213