correctly calculate binlog index path during binlog_change_to_binlog

Summary:
During promotion(binlog_change_to_binlog), the binary index file path is calculated incorrectly due to opt_binlog_index_name is a file name without path(such as binary-logs-{port}.index) but `mysql_bin_log.open_index_file()` requires either pass full binlog index name as 1st parameter or use 2nd parameter to calculate full binlog index file path.

Use 2nd parameter(opt_bin_logname) to calculate full binlog index file path.

Reviewed By: bhatvinay

Differential Revision: D27703333

fbshipit-source-id: c4827dbc9bc

sql/binlog.cc

@@ -11744,7 +11744,9 @@ int binlog_change_to_binlog(THD *thd) {
   mysql_bin_log.close(LOG_CLOSE_INDEX, /*need_lock_log=*/false,
                       /*need_lock_index=*/false);
 
-  if (mysql_bin_log.open_index_file(opt_binlog_index_name, opt_bin_logname,
+  // Use opt_bin_logname to calculate index file full path
+  if (mysql_bin_log.open_index_file(/*index_file_name_arg*/ nullptr,
+                                    opt_bin_logname,
                                     /*need_lock_index=*/false)) {
     error = 1;
     goto err;