Travis stages are designed not to run after the first that fails. We
never used them for that, only for nicer presentation of
results. Running all tests independently of each other (e.g.: qemu and
doxygen) even when one fails is more important than presentation, so
reduce the number of stages to just two: "buildonly" and "tests"
Travis job name: doesn't look as good alone as when combined
with a stage name but it's enough to identify jobs.

Reducing to just one stage is tempting but it would require a lot more
naming surgery so let's start with this small diff and two stages for
now.

Signed-off-by: Marc Herbert <marc.herbert@intel.com>