Fix the flakyness for delete tests using docker image

[jacqueqa]

PetStore API is a public API, so everytime we use a random id to create a new pet, this id may be overridden by other API test users. This is causing flakiness on the tests.
By looking at the API repository, a possible solution would be to create a docker image to avoid the id overlapping.

https://github.com/swagger-api/swagger-petstore/blob/master/README.md