block/rbd: fix write zeroes with growing images

Commit d24f8023 ("block/rbd: increase dynamically the image size")
added a workaround to support growing images (eg. qcow2), resizing
the image before write operations that exceed the current size.

We recently added support for write zeroes and without the
workaround we can have problems with qcow2.

So let's move the resize into qemu_rbd_start_co() and do it when
the command is RBD_AIO_WRITE or RBD_AIO_WRITE_ZEROES.

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2020993
Fixes: c56ac27d

 ("block/rbd: add write zeroes support")
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20220317162638.41192-1-sgarzare@redhat.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>