Turn VIR_ERR_NO_DOMAIN and NO_NETWORK errors into Not_found exceptions.
-libvirt has added a few new calls since we last looked, particularly
-in the area around storage management. Need to add these.
+We should add a way to use the authentication mechanisms, like
+virConnectOpenAuth:
+http://www.redhat.com/archives/libvir-list/2008-April/msg00235.html