tests/acceptance: Add boot tests for some of the QEMU advent calendar images

tests/acceptance: Add boot tests for some of the QEMU advent calendar images

The 2018 edition of the QEMU advent calendar 2018 featured Linux images
for various non-x86 machines. We can use them for a boot tests in our
acceptance test suite.

Let's also make sure that we build the corresponding machines in Travis.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Liam Merwick <liam.merwick@oracle.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
Message-Id: <20200124170325.30072-1-thuth@redhat.com>
[PMD: Rebased, --python=python3 parameter dropped in commit 5311cb12e]
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>