MDEV-8469 Add RESET MASTER TO x to allow specification of binlog file nr

Other things:
- Avoid calling init_and_set_log_file_name() when opening binary log.
- Remove newlines early when reading from index file.
- Ensure that reset_logs() will work even if thd is 0 (Can happen on startup)
- Added thd to sart_slave_threads() for better error handling.

sql/sql_lex.h

@@ -2489,6 +2489,7 @@ public:
   USER_RESOURCES mqh;
   LEX_RESET_SLAVE reset_slave_info;
   ulonglong type;
+  ulong next_binlog_file_number;
   /* The following is used by KILL */
   killed_state kill_signal;
   killed_type  kill_type;