Fix normalization of FQDNs in DNS installer code.

https://fedorahosted.org/freeipa/ticket/3600
Handle a 501 in cert-find from dogtag as a "not supported"

Upgrading from d9 -> d10 does not set up the RESTful interface
in dogtag, they just never coded it. Rather than trying to backport
things they have decided to not support upgrades.

We need to catch this and report a more reasonable error. They are
returning a 501 (HTTP method unimplemented) in this case.

https://fedorahosted.org/freeipa/ticket/3549