Introduce back override for bad-format-string

It still happens on both Travis and Landscape, though I can not
reproduce it locally.

Signed-off-by: Michal Čihař <michal@cihar.com>
Merge branch 'master' into bootstrap
Upgrade pylint configuration

Signed-off-by: Michal Čihař <michal@cihar.com>
Merge branch 'master' into bootstrap