catches exception where valid AWS keys are provided but user has not added any AWS services or provided credit card.

- A credit card is needed to verify account for AWS access keys
- This catches this error which may affect people who first sign up through the Amazon Mechanical Turk website (as opposed to http://aws.amazon.com)
- The warning message points people to the relevant docs
- Otherwise continues as though the AWS keys are invalid/not entered correctly.
- Tested with an dummy account that had keys but did not have credit card.