Fix to #622, http://bugs.skysql.com/show_bug.cgi?id=622

When MaxScale starts it opens log file of each type and if there exist log files of same types in the same directory, it will try to reuse the file with largest sequence number in it. If there are no existing files, a file name with sequence number 1 will be created. If the file with largest sequence number is not writable, a new log file with larger sequence number will be created.
Merge branch 'develop' of https://github.com/mariadb-corporation/MaxScale into develop