rgw, cls_rgw: add bi put

An admin operation to set bucket index entries.

Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>
osd: fix filter_prefix scoping in omap_get_vals

filter_prefix should only affect the case where it's greater than
start_after, otherwise we'll end up with a key equals to start_after.

Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>
formatter: no need for dynamic allocation

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