Replaced 'swagger.yaml' with openapi.yaml. Refer to b/32670418.
Replaced 'swagger.yaml' with openapi.yaml. Refer to b/32670418.

GoogleCloudPlatform/endpoints-samples,GoogleCloudPlatform/endpoints-samples,GoogleCloudPlatform/endpoints-samples,GoogleCloudPlatform/endpoints-samples,GoogleCloudPlatform/endpoints-samples,GoogleCloudPlatform/endpoints-samples