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>

ipaserver/install/ipa_cacert_manage.py

@@ -521,7 +521,7 @@ class CACertManage(admintool.AdminTool):
             for ca_nickname, _trust_flags in loaded:
                 if ca_nickname == nickname:
                     continue
-                elif ipa_ca_nickname == nickname:
+                if ipa_ca_nickname == nickname:
                     raise admintool.ScriptError(
                         "The IPA CA cannot be removed")
                 logger.debug("Verifying %s", ca_nickname)

ipatests/test_integration/base.py

@@ -77,7 +77,7 @@ class IntegrationTest:
         else:
             domain_level = cls.master.config.domain_level
 
-        if cls.master.config.fips_mode:
+        if cls.master.config.fips_mode:  # pylint: disable=using-constant-test
             cls.fips_mode = True
         if cls.fips_mode:
             cls.enable_fips_mode()