rgw-admin, cls_rgw: add bi_get objclass operation

Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>
common, rgw: json escaping gets input buf size

We now deal with strings that embed a null character.

Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>
cls_rgw: add missing flags encoding to rgw_bucket_dir_entry::dump()

Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>