tests/functional: Skip the screendump tests if the command is not available

It is possible nowadays to compile QEMU without pixman support - in that
case the screendump command is not available and the related tests fail.
Thus skip these tests if the screendump command could not be executed.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20250325081713.283490-2-thuth@redhat.com>
3 files changed