travis-ci: Add test.py for various qemu platforms

- Add a PPA for a more recent qemu (required for PowerPC to work)
- Add tests to run test.py for various QEMU platforms.  This relies on
  swarren's uboot-test-hooks repository to provide the abstractions.

Acked-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Tom Rini <trini@konsulko.com>