Adding a list of attibutes to be used during checkout of custom recipes.

It would be nice if AWS OpsWorks allowed for custom attributes to be set with the subversion provider. This causes an issue when trying to retrieve cookbooks from a subversion repository with a self-signed SSL certificate which can usually be accessed using `--trust-server-cert`.

The default attribute setting is set to match what is defined in:
https://github.com/opscode/chef/blob/master/lib/chef/resource/subversion.rb