Support primitive zeroes in restJson and restXml (#451)

* suppress serializing of primitive 0s as struct members

When a struct primitive is a "zero value" it shouldn't be serialized. It's frequently the case that `0` is an invalid input & sending 0 on the wire will actually cause the service to reject the request.

Fixes #439

* support primitive zeros in restJson and restXml

1. Avoid serializing PrimitiveInteger when it is 0, unless it is required
2. Setup the ability to write protocol tests against generated SDKs
3. Fix a trailing `,` in aws-sdk-codegen-test
4. Keep trying to get the gradle build to invalidate caches properly.

* Add awsQuery support

* Cleanups

* Fix bad merge

* Fix clippy error