title: Unable to filter on AWS RDS stack-name
body: <p>Why doesn't this just work? Pulling the tags listed with my rds instance:</p>
  
  <pre><code>aws rds list-tags-for-resource --resource-name arn:aws:rds:eu-central-1:12345678901:db:pa1jyg4oc56mipf
  
  {
      "TagList": [
          {
              "Value": "DatabaseRdsInstance",
              "Key": "aws:cloudformation:logical-id"
          },
          {
              "Value": "production-test-123",
              "Key": "aws:cloudformation:stack-name"
          },
          {
              "Value": "arn:aws:cloudformation:eu-central-1:12345678901:stack/production-test-123/1234abc-56f9-11e5-b10e-50d501fbb66e",
              "Key": "aws:cloudformation:stack-id"
          }
      ]
  }
  </code></pre>
  
  <p>Filtering on one of those tags fails:</p>
  
  <pre><code>aws rds describe-db-instances --filters Name="tag:aws:cloudformation:stack-name",Values=production-test-123
  A client error (InvalidParameterValue) occurred when calling the DescribeDBInstances operation: Unrecognized filter name: tag:aws:cloudformation:stack-name
  </code></pre>
  
  <p>Nor does it work when I leave the <code>tag</code> part from the Name:</p>
  
  <pre><code>aws rds describe-db-instances --filters Name="aws:cloudformation:stack-name",Values="production-test-123"
  
  A client error (InvalidParameterValue) occurred when calling the DescribeDBInstances operation: Unrecognized filter name: aws:cloudformation:stack-name
  </code></pre>
  
  <p>What am I missing here?</p>