MDEV-8670 main.mdev-504 fails on Windows (in buildbot and outside)

Test failed because it hit net_write_timeout. It might happen in
different circumstances, and that's not what the testcase tests,
so the timeout is now set to a bigger value.

mysql-test/r/mdev-504.result

+SET GLOBAL net_write_timeout = 900;
 CREATE TABLE A (
 pk INTEGER AUTO_INCREMENT PRIMARY KEY,
 fdate DATE
@@ -19,3 +20,4 @@ DROP TABLE A;
 DROP PROCEDURE p_analyze;
 DROP FUNCTION rnd3;
 SET GLOBAL use_stat_tables = DEFAULT;
+SET GLOBAL net_write_timeout = DEFAULT;

mysql-test/t/mdev-504.test

 --disable_ps_protocol
 
+SET GLOBAL net_write_timeout = 900; 
+
 CREATE TABLE A (
   pk INTEGER AUTO_INCREMENT PRIMARY KEY,
   fdate DATE
@@ -74,4 +76,4 @@ DROP TABLE A;
 DROP PROCEDURE p_analyze;
 DROP FUNCTION rnd3;
 SET GLOBAL use_stat_tables = DEFAULT;
-
+SET GLOBAL net_write_timeout = DEFAULT;