Enhancement: the URI to the Jenkins Server in Docker for IT-Tests should be configurable

Currently the URI for the Jenkins Server in Docker is hardcoded in com.offbytwo.jenkins.integration.Constants. This works well in Linux & MacOS but fails on Windows (7) as the Docker container runs in a VirtualBox and therefore with a different IP address.

It would be required to override this URI from a command line parameter so that the tests can be executed on Windows without changing the code. If no parameter is specified, the currently configured URI constant should be used as default.