rgw: multi object delete supports versioning

Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>
cls/rgw: when removing delete marker, clean up instance entry

Since we create the instance entry at the bucket index, we should also
remove it. Otherwise we end up with objects that have bucket index
entries, but don't have olh. In these cases we'll be failin operations
on these objects, as their bucket index olh tag will always mismatch the
actual object olh tag.

Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>
rgw: when deleting object version return -ENOENT if needed

If can't do bi_get() on the object, we should treat it as non existent
and just return.

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