tests/qtest: arm: fix operation in a build without any boards or devices

ARM/aarch64 are easy to fix because they already have to pass a machine
type by hand.  Just guard the tests with a check that the machine actually
exists.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20240509170044.190795-14-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
3 files changed