remove escape sequences in log (capture a traceback)

[jedie]

A traceback contains escape sequences in log files, e.g.:

ERROR 2020-03-06 07:47:03,718 _______________________________________________________________________________
ERROR 2020-03-06 07:47:03,718 ERROR: Backup aborted with a unexpected error:
ERROR 2020-03-06 07:47:03,718 �[31mTraceback (most recent call last):�[0m
ERROR 2020-03-06 07:47:03,718   File "/home/jens/repos/PyHardLinkBackup/pyhardlinkbackup/phlb/main.py", line 349, in backup
ERROR 2020-03-06 07:47:03,718 �[37m�[1m    stats_helper = backup_worker.process()�[0m
...