ansible: fedmsg-hub-3 support

[Adam Williamson]

hey folks! just wanted to pass along a note about this change I made to
the infra scripts today:

https://infrastructure.fedoraproject.org/cgit/ansible.git/commit/?id=6c390c6...

What I did was extend a bit of scaffolding that already exists to
handle fedmsg deployment differently if the host is in a group with
'python34-fedmsg' in its name (the 'python34' there is a EL-ism, but I
didn't want to change it) so it now also covers fedmsg-hub as well as
fedmsg-base.

Now, if a system is in a group with 'python34-fedmsg' in its name and
the 'fedmsg/hub' role is run on that system, instead of enabling the
'fedmsg-hub' service, it'll enable the 'fedmsg-hub-3' service. The
'restart fedmsg-hub' handler is also tweaked so it conditionally
restarts *both* 'fedmsg-hub.service' *and* 'fedmsg-hub-3.service' (this
seemed like the easiest solution to the service restart problem; as
we're using conditional-restart.sh, whichever isn't present will just
be ignored).

This should help with moving things from Python 2 fedmsg to Python 3
fedmsg. It should be relatively easy to extend to the other fedmsg
roles too, if desired - I didn't do that as I didn't want to change too
much, and fedmsg-hub is all I needed for the box I'm migrating.

Please let me know if you have any comments, concerns or suggestions
about this, thanks! I did ask around on IRC and it didn't seem like
anyone had a better idea or plan for doing this, so I just went
ahead...