Tests fail when multiple instances run at the same time

Steps to reproduce:
1. Start an Opencast instance
2. Build a seperate Opencast

Actual Results:
module tests for matterhorn-kernel may fail with for example:
TrustedHttpClientResourceClosingTest.testResourceClosing:61->startServer:71 » Bind

Expected Results:
Tests should not be influenced by running instances

For Testing a instance should start with a non standard and free port and use generated names for temporary files.