Fixes some Coverity issues
ipadiscovery.py: added assert should universe break
plugins/dns.py: removed dead code
dnssec/ldapkeydb.py: attribute assert in the proper object
test_automount_plugin.py: fixed possible close() on None
xmlrpc_test.py: Coverity does not like accessing None.__class__
https://fedorahosted.org/freeipa/ticket/5661
Reviewed-By: Jan Cholasta <jcholast@redhat.com>
Reviewed-By: Martin Basti <mbasti@redhat.com>