This adds an upgrade variant of the FreeIPA tests, with only
the simplest client enrolment (sssd) for now. The server test
starts from the N-1 release and deploys the domain controller
role. The client test similarly starts from the N-1 release
and, when the server is deployed, enrols as a domain client.
Then the server upgrades itself, while the client waits (as the
server is its name server). Then the client upgrades itself,
while the server does some self-checks. The server then waits
for the client to do its checks before decommissioning itself,
as usual. So, summary: *deployment* of both server and client
occurs on N-1, then both are upgraded, then the actual *checks*
occur on N.
In my testing, this all more or less works, except the role
decommission step fails. This failure seems to be a genuine one
so far as I can tell; I intend to file a bug for it soon.