[Clojure] Add more complex spec tests to run the generator on

Created by: f-f

Description

As we figured out in #122, the current Petstore spec is not enough to test all the edge cases of the generator.

Suggest a fix/enhancement

As @wing328 suggested in https://github.com/OpenAPITools/openapi-generator/pull/122#issuecomment-403228826, we should start testing on the fake petstore spec.

Rough list of things to do for this issue:

• add a line to bin/clojure-petstore.sh to test against that new spec
• add Clojure tests in samples/client/fake-petstore/clojure/test/