Separate output destination of samples generated from OAS3

Created by: ackintosh

Description

Related comment: https://github.com/OpenAPITools/openapi-generator/issues/80#issuecomment-389748804

I think that the scripts under bin/openapi3 should output its results into samples/openapi3.

Currently, only PHP is following the rule above:

• OAS2
  • https://github.com/OpenAPITools/openapi-generator/tree/master/samples/client/petstore/php
• OAS3
  • https://github.com/OpenAPITools/openapi-generator/tree/master/samples/openapi3/client/petstore/php

The samples of same lang will have differences if those have generated from different OAS version. As supporting the OAS3 specific features progresses, differences between the samples from OAS2 and OAS3 becomes bigger.

Existing the difference between the samples from OAS2 and OAS3 is correct. so I think the samples should be put each appropriate location separately.