Description of problem:

There's a corner case with the new libvirtd feature to "remember" guests when it is restarted.  Take the following example:

1.  virDomainDefineXML on src
2.  virDomainStart on src
3.  virDomainMigrate on src -> migrates guest to dest
4.  Shut-down libvirtd on dest
5.  Restart libvirtd on dest

After step 5, you would expect libvirtd to "remember" the migrated guest, but at present, it does not.  DanB says this is because it is a "transient" guest, so doesn't have an /etc/libvirt/qemu config file.  It does, however, have a /var/run/libvirt/qemu state and pid file, so we could scan the entire directory looking for transient guests as well.