rbd: remove Rbd prefix from constants and provide aliases
rbd: remove Rbd prefix from constants and provide aliases

Image option constants are now named ImageOptionX, without an Rbd
prefix. Aliases to the old names are provided and doc comments for both.

Signed-off-by: John Mulligan <eda8ad33169deab44f9fe65847f99e368da6c91b@redhat.com>

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