rgw: convert plain object to versioned (with null version) when removing

rgw: convert plain object to versioned (with null version) when removing

Fixes #15243

When removing a plain null versioned object (was created prior to bucket versioning
enabled), need to convert the bucket index representation to a versioned one. This
is needed so that all the versioning mechanics play together.

Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>
(cherry picked from commit c6334d430b17739fed2df2b4481ae395ef6568d9)

Conflicts:
        src/rgw/rgw_rados.cc
          - hammer is missing get_zone() API from which log_data can be
            obtained. Needed to fall back to zone_public_config
            structure in bucket_index_unlink_instance() definition.
          - olh_tag string parameter added to
            bucket_index_unlink_instance() definition.
        src/rgw/rgw_rados.h
          - olh_tag string parameter added to
            bucket_index_unlink_instance() declaration.