Make linux headless UI testing more configurable
Summary: xvfb-run wrapper options can now be passed as CMake option, default is unchanged
Test Plan: Dashboard
Reviewers: kislinsk, O1 MITK Reviewer Group I
Reviewed By: kislinsk, O1 MITK Reviewer Group I
Maniphest Tasks: T27367
Differential Revision: https://phabricator.mitk.org/D292