go fmt
dynamodb: Drop 'Value' key from AttributeUpdates with 'DELETE' Action

See http://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_UpdateItem.html#API_UpdateItem_RequestSyntax
dynamodb: Rework on integration and unit tests with gocheck
Merge pull request #61 from nabeken/dynamodb-gocheck

dynamodb: Rework on integration and unit tests with gocheck