Failed to get connection to session: Failed to connect to socket /tmp/dbus: Connection refused (virt-manager)

Problem: 
  virt-manager cannot be started after fresh install due to a bug on dbus.

Fix, recreate machine id: 
  dbus-uuidgen > /var/lib/dbus/machine-id

Ref: 
  http://bugs.centos.org/view.php?id=5334
  https://bugzilla.redhat.com/show_bug.cgi?id=598200
  http://nutanix.blogspot.com/2013/06/kvm-virt-manager-startup-failure.html