Remove unused variables in the code

This commit removes unused variables or rename variables as "expected to
be unused" by using "_" prefix.

This covers only cases where fix was easy or only one unused variable
was in a module

Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>
Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>

ipaserver/install/installutils.py

@@ -1021,7 +1021,7 @@ def load_external_cert(files, subject_base):
         ca_subject = DN(('CN', 'Certificate Authority'), subject_base)
         ca_nickname = None
         cache = {}
-        for nickname, trust_flags in nssdb.list_certs():
+        for nickname, _trust_flags in nssdb.list_certs():
             cert = nssdb.get_cert(nickname, pem=True)
 
             nss_cert = x509.load_certificate(cert)