+1 on this. I was very excited to see 1.7 pop up after so long because it fixed a number of things, but we had to revert to 1.6 because of the not closing connections issue. With lots of start/stop on temporary slaves this winds up happening:
2013-02-24 03:59:54.919+0000: 32024: error : virNetServerDispatchNewClient:246 : Too many active clients (40), dropping connection from 127.0.0.1;0
Restarting Jenkins or libvirt solves the issue temporarily. Reverting back to 1.6 also solves the issue, so most likely a regression in 1.7. So far as we're concerned this is a show stopper bug as it renders Jenkins unusable.
This is on a RHEL6 x86_64, Jenkins version 1.502 (though also tested with 1.478).
Thanks for picking up this plugin!