This test doesn't even build QEMU, it just builds and runs all the
unit tests. Intended to make checking unit tests on all docker images
easier.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>