This will write log messages as plain text (no timestamp and other stuff
like PlainTextFormatter).
Warnings and errors will be prefixed accordingly.

Change-Id: Id82512d7dd3907a4c7cd69a963a375966189dc20
Reviewed-on: https://gerrit.libreoffice.org/62370
Tested-by: Jenkins
Reviewed-by: Samuel Mehrbrodt <Samuel.Mehrbrodt@cib.de>