Validate that IAM policy Resources are formatted as an ARN

[jpb]

Malformed ARNs in the IAM Policy Resource property produce the following CloudFormation error:

The policy failed legacy parsing (Service: AmazonIdentityManagement; Status Code: 400; Error Code: MalformedPolicyDocument ...)

Example malformed ARNs:

• arn:aws:ssm:::session/${aws:username}-*
• arn:aws:ssm:*:*session/${aws:username}-*

Valid:

• arn:aws:ssm:*:*:session/${aws:username}-*