Add full android test support

~~Should https://github.com/snipsco/dinghy be used?~~

Support for testing android binaries that depends only on libc was added in https://github.com/japaric/cross/pull/132.

We should add support to test android binaries in the android emulator. See https://github.com/japaric/cross/pull/132 for a brief discussion of the issues of distributing the android emulator.