Dependency inject Retrofit client to simplify api declaration

Dependency inject Retrofit client to simplify api declaration

- centrally declare AAI rest client [0]
- add integration test to assert http request to AAI
- do not ignore test failure

[0] this has the advantage, that
- headers are defined for all requests via interceptor
- this is the correct setup to add tracing to the app with a later change
- credentials for AAI can be centrally configured (it is now configurable in the latest AAI version)

Issue-ID: USECASEUI-857
Change-Id: I5ef0e859e3bc2ab4b42fe6ed27632c211b90ac62
Signed-off-by: Fiete Ostkamp <Fiete.Ostkamp@telekom.de>