Show hidden/blacklisted OSes in cluster info

Since we can blacklist/hide non-existing OSes (for preseeding), we
cannot query easily the OSes themselves for this status. Hence we
export the entire lists in cluster info (which should be cheaper than
gnt-os diagnose).

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>