Fix open_close_connections

The assumption that errno would be the same for the duration of the whole
call chain is wrong as it's possible that other calls that modify it are
made. Using the actual error string itself is much more reliable.

system-test/open_close_connections.cpp

@@ -21,7 +21,7 @@ void query_thread(TestConnections& test, int thread_id)
                         mariadb_get_infov(conn, MARIADB_CONNECTION_PORT, &port);
                         mariadb_get_infov(conn, MARIADB_CONNECTION_HOST, &host);
 
-                        test.expect(mysql_errno(conn) == 0 || errno == EADDRNOTAVAIL,
+                        test.expect(mysql_errno(conn) == 0 || strstr(mysql_error(conn), "system error: 110")
                                     "Error opening conn to %s:%u, thread num is %d, iteration %ld, error is: %s\n",
                                     host, port, thread_id, i, mysql_error(conn));