rbd: don't cap the buffer size used in GetImageNames
rbd: don't cap the buffer size used in GetImageNames

This removes the limit on the max buffer size GetImageNames is willing to pass
to rbd_list2, which is somewhat arbitrary and is too small for large clusters.
GetImageNames will continue to start with a small buffer size and retry with a
larger buffer if rbd_list2 returns ERANGE (just without a cap on the max buffer
size it's willing to go to).

Signed-off-by: Sanford Miller <3436e170c9a0b84ab30cb4c0dacf0efe17e13dfa@digitalocean.com>

ceph/go-ceph,ceph/go-ceph,ceph/go-ceph