Comment 2 for bug 1129436

Actually I think this was due to having automatic updates run on the slave. We used to have unattended upgrades running everywhere which could interfere with dpkg as run by devstack. We have fixed this by disabling unattended upgrades on our single use slaves as they have new images rebuilt daily. This fix was in openstack-infra/config I3989c9e6ad9469f441ca5d3627f7b3b704d8a8da change.