lint: Make Pylint-2.4 happy again
    
    This is the first time running Pylint-2.4 over the whole IPA codebase.
    ```
    Pylint on /usr/bin/python is running, please wait ...
    internal error with sending report for module ['ipaserver/plugins/serverroles.py']
    maximum recursion depth exceeded while calling a Python object
    ************* Module ipatests.test_integration.base
    ipatests/test_integration/base.py:84: [W0125(using-constant-test), IntegrationTest.install] Using a conditional statement with a constant value)
    ************* Module ipaserver.install.ipa_cacert_manage
    ipaserver/install/ipa_cacert_manage.py:522: [R1724(no-else-continue), CACertManage.delete] Unnecessary "elif" after "continue")
    ```
    
    The latest Pylint (via the Tox task) checks only:
    ```
    {envsitepackagesdir}/ipaclient \
    {envsitepackagesdir}/ipalib \
    {envsitepackagesdir}/ipapython
    ```
    
    , while the distro-Pylint runs over all project but it is not fresh.
    That's why these warnings/errors weren't exposed before now.
    
    Concerning `internal error`: a fix was accepted by upstream:
    https://github.com/PyCQA/pylint/issues/3245, but wasn't released yet.
    Until that is done, Pylint just warns.
    
    Related: https://pagure.io/freeipa/issue/8116
    Signed-off-by: Stanislav Levin <slev@altlinux.org>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>