Install/upgrade buildozer master before running, fixes #630

Installs missing buildozer dependency from master before running buildozer android release. Note that we're currently relying on the master branch since it adds a couple of fixes required for building a release. In another iteration we could think of sandboxing the buildozer (and other deps) in a virtualenv. That would make it possible for app.id to fine grain their requirements without messing up with other dependencies.