package systemd 219-7ubuntu6 failed to install/upgrade: timed out starting policykit

Possibly the same as Bug 1446219, but reporting anyhoo.

This occurred when I did `telinit 1` and then `sudo apt-get install byobu` on a freshly-installed-that-day Ubuntu GNOME 15.04 system.

Non-Ubuntu packages on this host:
  * google-chrome-stable
  * vagrant (from upstream)

ProblemType: Package
DistroRelease: Ubuntu 15.04
Package: systemd 219-7ubuntu6
ProcVersionSignature: Ubuntu 3.19.0-39.44-generic 3.19.8-ckt9
Uname: Linux 3.19.0-39-generic x86_64
ApportVersion: 2.17.2-0ubuntu1.8
Architecture: amd64
Date: Wed Dec 16 07:33:03 2015
DuplicateSignature: package:systemd:219-7ubuntu6:subprocess installed post-installation script returned error exit status 1
ErrorMessage: subprocess installed post-installation script returned error exit status 1
InstallationDate: Installed on 2015-12-16 (0 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422)
MachineType: LENOVO 20AQCTO1WW
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-3.19.0-39-generic.efi.signed root=/dev/mapper/ubuntu--vg-root ro noprompt quiet splash vt.handoff=7
RelatedPackageVersions:
 dpkg 1.17.25ubuntu1.1
 apt 1.0.9.7ubuntu4.2
SourcePackage: systemd
Title: package systemd 219-7ubuntu6 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1
UdevLog: Error: [Errno 2] No such file or directory: '/var/log/udev'
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 10/20/2014
dmi.bios.vendor: LENOVO
dmi.bios.version: GJET80WW (2.30 )
dmi.board.asset.tag: Not Available
dmi.board.name: 20AQCTO1WW
dmi.board.vendor: LENOVO
dmi.board.version: 0B98417 PRO
dmi.chassis.asset.tag: No Asset Information
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.version: Not Available
dmi.modalias: dmi:bvnLENOVO:bvrGJET80WW(2.30):bd10/20/2014:svnLENOVO:pn20AQCTO1WW:pvrThinkPadT440s:rvnLENOVO:rn20AQCTO1WW:rvr0B98417PRO:cvnLENOVO:ct10:cvrNotAvailable:
dmi.product.name: 20AQCTO1WW
dmi.product.version: ThinkPad T440s
dmi.sys.vendor: LENOVO