Unify string formatting

Use one way of string formatting: replace old `%` style with new `str.format`.

Resolve #855.
3 jobs for cleanup/string-formatting in 1 minute and 4 seconds (queued for 13 seconds)
latest
Status Job ID Name Coverage
  Test
passed #8511
pycodestyle

00:00:15

passed #8510
shellcheck

00:00:27

passed #8512
unit_tests

00:00:21