Make lint work on Fedora 22.
pylint added 'confidence' parameter to 'add_message' method of PyLinter.
To be compatible with both, pre- and post- 1.4 IPALinter must accept
the parameter but not pass it over.
Also python3 checker was added and enabled by default. FreeIPA is still
not ready for python3.
Additionally few false-positives was marked.
Reviewed-By: Martin Basti <mbasti@redhat.com>