Upgrade API client integration tests to use Fake Petstore spec

[wing328]

Description

petstore-with-fake-endpoints-models-for-testing.yaml covers a lot more edge cases when comparing with the original one (petstore.yaml)

We'll need to to update petstore.yaml with petstore-with-fake-endpoints-models-for-testing.yaml so to ensure the edge cases are covered moving forward.

API clients using petstore-with-fake-endpoints-models-for-testing.yaml:

• Android
• Bash
• C++ (qt5, cpprest, tizen)
• C#
• Clojure
• Dart
• Elixir
• Flash
• Go
• Groovy
• JavaScript
• Java
• ObjC
• Perl
• PHP
• Python
• Ruby
• Swift (2.x ◻️, 3,x ✅)
• Scala

If anyone wants to work on the enhancement, please reply to let us know. Thank you!

[akhilkedia]

I'll update the tizen client gen in a week or two.