Fix to MXS-63: https://mariadb.atlassian.net/browse/MXS-63

Maxkeys and maxpasswd now use MAXSCALE_HOME or the default installation directory if MAXSCALE_HOME is not set.
If all else fails, /tmp/ is used for logging.

server/core/gateway.c

@@ -826,6 +826,7 @@ static bool file_is_readable(
                         absolute_pathname,
                         eno,
                         strerror(eno))));
+		LOGIF(LE,(skygw_log_sync_all()));
                 succp = false;
         }
         return succp;