Patch providers for absent my.cnf

If the /root/.my.cnf file does not exist but is specified by the
`--defaults-file` argument, the mysql calls will fail. The
`mysql::config` class creates this file, but if the custom resources are
used without including our classes then it will still break.

This allows users to use our custom resources without having to use our
classes.
Updating specs for .my.cnf
Add tests for absent /root/.my.cnf
Merge pull request #141 from hunner/optional_my.cnf

Patch providers for absent my.cnf