Created Process Manager Test API

Hi,

I extracted (and documented) testing API I've been using to test my Spring Boot demo to a separated jar. Now folks can import `process-test` jar and extend `AbstractProcessTest` class in their integration tests.

My testing API deals with some common issues related to the testing of Fabric8 managed process:
- creating pre-configured `ProcessManagerService`
- making sure that spawned processes are killed after the tests (in order to avoid processes leaking on CI servers)
- detecting moment when started process is ready to be tested (usually when Spring context has been properly initialized) without using `Thread.sleep` antipattern
- providing REST template to communicate with the spawned microservice
- more cool stuff to be added

Cheers.