Make AWS::DynamoDB use legacy client.

The higher level abstractions provided for DynamoDB only work fully with
the legacy version of the low-level client. This change forces the higher
level abstractions to fall back to the legacy client API, but allows use of
the new client-level API directly.
Test failure fixes for DynamoDB.

The way we dealt with the configuration in the previous change on
DynamoDB clients had knock on effects to clients of, for example,
Simple Email Service. Fixed those, and updated tests for DynamoDB
to handle the different way we instantiate its client.
Merge pull request #343 from aws/dynamodb-hl-versioning

Make AWS::DynamoDB use legacy client.