qemu.tests.multi_disk: Add check_guest_proc_scsi flag for linux guests

Check guests proc scsi only support Linux guests, so add a flag to check
it when using virtio-scsi.

Check guests proc scsi only support Linux guests, so disable for
Windows guests.

Signed-off-by: Shuping Cui <scui@redhat.com>
qemu.tests.cfg: Update cfg for multi_disk

Signed-off-by: Shuping Cui <scui@redhat.com>