qemu-img: There is more than one host device driver

I haven't heard yet of anyone using qemu-img to copy an image to a real floppy,
but it's a valid use case.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

block_int.h

@@ -117,6 +117,9 @@ struct BlockDriver {
     /* Returns number of errors in image, -errno for internal errors */
     int (*bdrv_check)(BlockDriverState* bs);
 
+    /* Set if newly created images are not guaranteed to contain only zeros */
+    int no_zero_init;
+
     struct BlockDriver *next;
 };