pylint: Fix several warnings

Fixes Pylint warnings:
- R1729(use-a-generator)
- R1710(inconsistent-return-statements)
- R1727(condition-evals-to-constant)

Fixes: https://pagure.io/freeipa/issue/8772
Signed-off-by: Stanislav Levin <slev@altlinux.org>
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>

ipalib/install/kinit.py

@@ -63,6 +63,8 @@ def kinit_keytab(principal, keytab, ccache_name, config=None, attempts=1):
             else:
                 os.environ.pop('KRB5_CONFIG', None)
 
+        return None
+
 def kinit_password(principal, password, ccache_name, config=None,
                    armor_ccache_name=None, canonicalize=False,
                    enterprise=False, lifetime=None):