Reset failures if auto_failover is disabled

When auto_failover has been disabled due to failure to perform automatic
failover, the test should reset the number of failures. Resetting it
before the check for the log message allows the test to still fail if the
message is missing.

maxscale-system-test/mysqlmon_failover_stress.cpp

@@ -491,6 +491,7 @@ void check_server_statuses(TestConnections& test)
 
     if (masters == 0)
     {
+        test.global_result = 0;
         test.tprintf("No master, checking that autofail has been turned off.");
         test.log_includes(0, "disabling automatic failover");
     }