tests/acceptance: Add boot tests for sh4 QEMU advent calendar image

Now that we can select the second serial console in the acceptance tests
(see commit 746f244d "Allow to use other serial consoles than default"),
we can also test the sh4 image from the QEMU advent calendar 2018.

Message-Id: <20200515164337.4899-1-thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>