[plotterparameter] Don't use f string yet

The processing nodes are not on Python 3.6 yet
therefore these can not be used.

The other uses are only related to tests and
tasks not done on the processing nodes.
4 jobs for clean_f_string in 16 minutes and 38 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #191675
docker-build
build_linux_36

00:13:50

64.0%
passed #191676
docker-build
build_linux_37

00:13:50

64.0%
passed #191673
macosx
build_macosx_36

00:16:33

64.0%
passed #191674
macosx
build_macosx_37

00:16:32

64.0%