[CI] Change fake service tests to integration tests #61

We are using doubles tests as our primary unit testing mechanism now (spec/hcloud/ and spec/doubles/). We are planning to keep the older fake service tests and use them as integration tests for the real API.

At the moment they are in the folder spec/integration/, but still behave in the old way using the fake service from spec/fake_service/. We want to completely delete the fakes in spec/fake_service/ and instead use the real API for testing.

A quick first test showed that this will require several adjustments to the code, because currently the tests expect to start in a clean project with 0 other resources. This is not granted in the CI project. We have to make sure that tests also work when there are already other resources in the cloud project.