Fix ipa-replica-prepare's error message about missing local CA instance
ipa-replica-prepare must be run on a replica with CA or all the certs
needs to be provided (for CA-less case).
The old messages were utterly confusing because they mixed errors about
missing certs and missing local CA instance into one text.
https://fedorahosted.org/freeipa/ticket/6134
Reviewed-By: Martin Basti <mbasti@redhat.com>
Reviewed-By: Ben Lipton <blipton@redhat.com>