Validate API-level tests against Swagger spec

The goal is to include validation of requests and responses (maybe only responses) in *ApiTests which are mostly located under whisk/core/controller package in the test suite. This validation is already in place for the tests in system.basic package.

## Provide the expected results and outputs:

The validator should check that request and response conforms to the Swagger spec in core/controller/src/main/resources/apiv1swagger.json

## Additional information you deem important:
Some test from the system.basic test suite might be later moved to the API-level tests as long as we have the swagger spec validation in place.