tests/acceptance: Add a boot test for the xlnx-versal-virt machine

tests/acceptance: Add a boot test for the xlnx-versal-virt machine

As described by Edgar here:

 https://www.mail-archive.com/qemu-devel@nongnu.org/msg605124.html

we can use the Ubuntu kernel for testing the xlnx-versal-virt machine.
So let's add a boot test for this now.

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Message-id: 20200525141237.15243-1-thuth@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>