Use an active fedmsg socket instead of passive ones.

This will cause trac to call out to an instance of fedmsg-relay running
somewhere.

This is preferable over binding to our own sockets because trac's
component management system re-instantiates our plugin for every http
request (I didn't think it did that before...).
Merge pull request #2 from fedora-infra/feature/active-instead-of-passive

Use an active fedmsg socket instead of passive ones.