Document that domain controller requires a static IP

[sgallagher]

The FreeIPA domain controller can be a little finicky if its IP address changes unexpectedly. Best practice therefore is to set a static IP address. If we are asked to deploy the domain controller on a machine that has a DHCP-assigned address, we should use the NetworkManager API to set that IP statically (and persistently) as part of the deployment process.

This will alleviate issues like that in the Fedora 22->23 upgrade where the interface names changed and DHCP-assigned addresses (such as those in KVM virtual machines) change, causing resolution issues.

[sgallagher]

Converting this to a doc bug. After conversation at our weekly meeting, it seems like there are too many edge-cases to consider here. We'll update the man page to indicate that the Domain Controller must retain a static IP address.