rgw: CompleteMultipart applies its olh_epoch

RGWCompleteMultipart was using get_system_versioning_params() to read an
olh_epoch, but was never applying it to the bucket index operation

Signed-off-by: Casey Bodley <cbodley@redhat.com>
(cherry picked from commit e4d1cc1)

src/rgw/rgw_op.cc

@@ -5748,6 +5748,7 @@ void RGWCompleteMultipart::execute()
   obj_op.meta.flags = PUT_OBJ_CREATE;
   obj_op.meta.modify_tail = true;
   obj_op.meta.completeMultipart = true;
+  obj_op.meta.olh_epoch = olh_epoch;
   op_ret = obj_op.write_meta(ofs, accounted_size, attrs);
   if (op_ret < 0)
     return;