* identity: Autodetect FreeIPA server with DNS
This adds the ability for the freeIPA related modules to be able to
auto-detect the IPA server through DNS.
This takes advantage of the fact that a lot of FreeIPA deployments
configure their hosts to use IPA as the nameserver.
This check is only used if we didn't set neither the ipa_host parameter,
nor the environment variable IPA_HOST.
* identity: Specify docs for DNS discovery of ipa_host
These docs specify that it can now default to DNS if the 'ipa-ca' entry
is available.
