Fix locate_config_file for Chef < 11.8

The change to a class method wasn't added until
Chef 11.8.x. This change will allow Chef 11
through 11.6 to work.

Fixes #13, #14
Fix the bug that config[:config_file] is overwriten
Merge pull request #16 from CaseCommonsDevOps/master

Fix locate_config_file for Chef < 11.8