MDEV-11540 Unexpected system threads in the process list

name innodb background threads as such

sql/sql_class.cc

@@ -796,6 +796,7 @@ THD::THD(my_thread_id id, bool is_wsrep_applier)
   mysql_audit_init_thd(this);
   net.vio=0;
   net.buff= 0;
+  net.reading_or_writing= 0;
   client_capabilities= 0;                       // minimalistic client
   system_thread= NON_SYSTEM_THREAD;
   cleanup_done= free_connection_done= abort_on_warning= 0;
@@ -4448,6 +4449,7 @@ MYSQL_THD create_thd()
   thd->store_globals();
   thd->set_command(COM_DAEMON);
   thd->system_thread= SYSTEM_THREAD_GENERIC;
+  thd->security_ctx->host_or_ip="";
   add_to_active_threads(thd);
   return thd;
 }

storage/innobase/handler/ha_innodb.cc

@@ -329,6 +329,7 @@ thd_destructor_proxy(void *)
 
 	thd_destructor_myvar = _my_thread_var();
 	THD *thd= create_thd();
+	thd_proc_info(thd, "InnoDB background thread");
 
 	mysql_mutex_lock(&thd_destructor_mutex);
 	thd_destructor_myvar->current_mutex = &thd_destructor_mutex;
@@ -1779,6 +1780,7 @@ innobase_create_background_thd()
 /*============================*/
 {
 	MYSQL_THD thd= create_thd();
+	thd_proc_info(thd, "InnoDB background thread");
 	THDVAR(thd, background_thread) = true;
 	return thd;
 }