MDEV-23787 mtr --rr fixes

1. rr record -h randomizes number of processors. Disable THREAD_POOL_SIZE check.

2. check for kernel.perf_event_paranoid for user-friendly error message.

mysql-test/include/mtr_check.sql

@@ -35,6 +35,7 @@ BEGIN
      AND variable_name != 'INNODB_BUFFER_POOL_LOAD_AT_STARTUP'
      AND variable_name not like 'GTID%POS'
      AND variable_name != 'GTID_BINLOG_STATE'
+     AND variable_name != 'THREAD_POOL_SIZE'
    ORDER BY variable_name;
 
   -- Dump all databases, there should be none