The larger memory limits on the Trusty beta will
hopefully make these less flaky.

Some of the dependencies for Android require 32-bit versions
of certain package, so add the architecture and update the package
database (via refresh: True) before installing them.

Use --filter to only download and extract necessary SDK components. This
is faster, uses less resources and gets around Travis disk space limits.
Update to latest SDK and NDK versions and use sha512 instead of sha1.
Use archive.extracted for better semantics and concision.