ACTS ART TEST for ckf tt-bar PU200: Multi-Thread approach

The ACTS ckf ART test for tt-bar PU200 is once again missing since a couple of days. Trying with a MT approach this time @adye

The reason we didn't use multi-thread before was because we wanted to monitor CPU time and memory in a single thread. But now that SPOT is running CKF we get that info from there