tests/qtest: Don't run cdrom boot tests if no accelerator is present

tests/qtest: Don't run cdrom boot tests if no accelerator is present

On a build configured with: --disable-tcg --enable-xen it is possible
to produce a QEMU binary with no TCG nor KVM support. Skip the cdrom
boot tests if that's the case.

Fixes: 0c1ae3ff9d ("tests/qtest: Fix tests when no KVM or TCG are present")
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-id: 20230508181611.2621-4-farosas@suse.de
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>