sheepdog: add missing .bdrv_has_zero_init

sheepdog: add missing .bdrv_has_zero_init

Commit 3ac21627 changed the behaviour of bdrv_has_zero_init() to default
to 0. In the review for Sheepdog it turned out that enabling it is safe,
so that commit updated one BlockDriver definition of sheepdog to use
bdrv_has_zero_init_1, missed however that there are more BlockDrivers in
the driver. Fix these now.

Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>
Reviewed-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>