Now that block drivers can support flags for .bdrv_co_truncate, expose
the parameter in the node level interfaces bdrv_co_truncate() and
bdrv_truncate().

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200424125448.63318-3-kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>