Address inconsistent-return-statements

Pylint warns about inconsistent return statements when some paths of a
function return None implicitly. Make all implicit returns either
explicit or raise a proper exception.

See: https://pagure.io/freeipa/issue/7758
Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>

install/share/wsgi.py

@@ -60,3 +60,4 @@ else:
         else:
             logger.error("IPA does not work with the threaded MPM, "
                          "use the pre-fork MPM")
+            raise RuntimeError('threaded MPM detected')