The test is based on bios-tables-test.c.  It creates a file with
the boot sector image and loads it into a guest using PXE and TFTP
functionality.

Cc: Jason Wang <jasowang@redhat.com>
Signed-off-by: NVictor Kaplansky <victork@redhat.com>
Suggested-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>