check_mysql does not respect !includedir directive in cnf file

[sawolf]

Originally appended to #383, which seems to be a separate issue:

My problem with check_mysql is that it's parsing the /etc/my.cnf file using its own parse logic that does not respect or understand !includedir statements. The /etc/my.cnf file supplied by MariaDB contains the following statement:
!includedir /etc/my.cnf.d
check_mysql does not interpret this statement or read the files nested therein. A nested config file is where I have a password=blah statement, which is never seen. If I replace the original /etc/my.cnf file with the contents of my nested file then check_mysql works. I shouldn't have to use a -f option to get check_mysql to only read my specific nested configuration file; ALL files in the hierarchy are significant.