Add support for MySQL SSLCA

In order to allow to SSLCA configuration with a MySQL database,
this commit adds support for adding the SSL CA key to the data bags.

[24805]
Remove unused database_config method

Remove an unused database_config method and clean up
whitespace.

[24805]
Use default value for MySQL sslca

- Refactor the default value for db_config.sslca to nil.
- Use `#respond_to_missing?` method which is the preferred method to use.

[24805]
Merge pull request #31 from sqm/24805-add-rds-file-resource-to-rubycas-server

#24805 - Add support for MySQL SSLCA