Added a test around creating a credit card as default.
Added a test around creating a credit card as default.

ronin1/braintree_dotnet,scottmeyer/braintree_dotnet,scottmeyer/braintree_dotnet,ronin1/braintree_dotnet,scottmeyer/braintree_dotnet,scottmeyer/braintree_dotnet,braintree/braintree_dotnet,braintree/braintree_dotnet,ronin1/braintree_dotnet