Update Android Guide (rough and dirty)

These changes correspond to travis-ci/travis-cookbooks#337

@BanzaiMan @joshk Please review and improve this draft. To be merged when the new VM image is available.

Following issues travis-ci/travis-ci#2279, travis-ci/travis-ci#2466, travis-ci/travis-ci#2470 and travis-ci/travis-ci#2476 can be closed when this new VM will be available.
This explained a bit below 

> For more flexibility, the licenses can be referenced with regular expressions (using Tcl syntax as expect command is used to automatically interact with the interactive prompts).

But feel free to make it even clearer.