Fix regression in test suite
32b1743e5fb318b226a602ec8d9a4b6ef2a25c9d introduced a regression in
test_serverroles.py, caused by ca_find attempting to log into the
Dogtag REST API. (ca_find is called by cert_find which is called by
server_del during cleanup).
Avoid logging into Dogtag in cert_find unless something actually
needs to be retrieved.
Fixes: https://fedorahosted.org/freeipa/ticket/6178
Reviewed-By: Martin Babinsky <mbabinsk@redhat.com>