mysql test: use OpenPort check over blind sleep

Changed files
+3 -1
nixos
+3 -1
nixos/tests/mysql-replication.nix
···
testScript = ''
$master->start;
$master->waitForUnit("mysql");
+
$master->waitForOpenPort(3306);
$slave1->start;
$slave2->start;
$slave1->waitForUnit("mysql");
+
$slave1->waitForOpenPort(3306);
$slave2->waitForUnit("mysql");
-
$slave2->sleep(100); # Hopefully this is long enough!!
+
$slave2->waitForOpenPort(3306);
$slave2->succeed("echo 'use testdb; select * from tests' | mysql -u root -N | grep 4");
'';
})