Add test for Swagger grammer

[simonredfern]

It should test the endpoint:

/obp/v1.4.0/resource-docs/v3.0.0/swagger

[hongwei1]

https://groups.google.com/forum/#!topic/swagger-swaggersocket/2lBT0qiZStU --> https://github.com/swagger-api/swagger-parser Only find this one. But not good enough, only check the basic grammer, and no clear error response...