Cleanup and add some CreditCardAttribute tests

[hughbe]

No description provided.

[stephentoub]

I'm not sure this is actually testing the same thing as was there previously. Setting these to null isn't the same as not setting them, e.g.

corefx/src/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/ValidationAttribute.cs

Lines 148 to 157 in d0dc5fc

	_errorMessage = value;
	_errorMessageResourceAccessor = null;
	CustomErrorMessageSet = true;
	// Explicitly setting ErrorMessage also sets DefaultErrorMessage if null.
	// This prevents subsequent read of ErrorMessage from returning default.
	if (value == null)
	{
	_defaultErrorMessage = null;
	}

[hughbe]

I see - I've fixed this

[stephentoub]

Other than my one comment, LGTM. Thanks for the cleanup.

[stephentoub]

Test Innerloop CentOS7.1 Debug Build and Test please
Test Innerloop Ubuntu14.04 Release Build and Test please