Update ElastiCache CodeGen test based on new SDK (#75)

ElastiCache would use new AWS SDK Go to include new features like LogDelivery which are currently not part of `elasticache-controller`. This PR updates the test data used in code generator for Elasticache tests.

Additionally I have updated `generator.yaml` to be inline with one being used in `elasticache-controller`. Updated unit tests which use `CacheCluster` resource to `ReplicationGroup`.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Author: nmvk