the DNS backends require many different params, it's just easier to
pass them all together and have backends do whatever.
For example, route53 API requires the fqdn. Some other backends require just the
"part" to insert.
* location - location in the database (where app is installed)
* zoneName - the dns zone name
* domain - domain in the database (where apps are installed into)
* name/getName() - this returns the name to insert in the DNS based on zoneName/location
* fqdn - the fully resolved location in zoneName
verifyDnsConfig also takes a domain object even if it's not in db just so that we can
test even existing domain objects, if required. The IP param is removed since it's not
required.
for caas, we also don't need the fqdn hack in dnsConfig anymore
