[artful] `sudo virt-manager` results in Gtk-WARNING **: cannot open display: :0

All gui apps fail to launch when using sudo, out-of-box, desktop 17.10 install. For example, gparted and virt-manager, which both require sudo, are not usable without a work-around.

#### Out-of-box experience
rbeisner@vistula:~⟫ sudo gedit
No protocol specified
Unable to init server: Could not connect: Connection refused

(gedit:32146): Gtk-WARNING **: cannot open display: :0

rbeisner@vistula:~⟫ xhost
access control enabled, only authorized clients can connect
SI:localuser:rbeisner

#### Work-around:

rbeisner@vistula:~⟫ xhost si:localuser:root
localuser:root being added to access control list

rbeisner@vistula:~⟫ xhost
access control enabled, only authorized clients can connect
SI:localuser:root
SI:localuser:rbeisner

rbeisner@vistula:~⟫ sudo gedit
rbeisner@vistula:~⟫ # (it launches ok)

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: x11-xserver-utils 7.7+7build1
ProcVersionSignature: Ubuntu 4.13.0-16.19-generic 4.13.4
Uname: Linux 4.13.0-16-generic x86_64
ApportVersion: 2.20.7-0ubuntu3
Architecture: amd64
CompizPlugins: No value set for `/apps/compiz-1/general/screen0/options/active_plugins'
CompositorRunning: None
CurrentDesktop: ubuntu:GNOME
Date: Thu Oct 19 00:49:13 2017
DistUpgraded: Fresh install
DistroCodename: artful
DistroVariant: ubuntu
GraphicsCard:
 Advanced Micro Devices, Inc. [AMD/ATI] Turks XT [Radeon HD 6670/7670] [1002:6758] (prog-if 00 [VGA controller])
   Subsystem: Hightech Information System Ltd. Turks XT [Radeon HD 6670/7670] [1787:2012]
InstallationDate: Installed on 2017-10-17 (1 days ago)
InstallationMedia: Ubuntu 17.10 "Artful Aardvark" - Beta amd64 (20171015)
MachineType: Gigabyte Technology Co., Ltd. To be filled by O.E.M.
ProcEnviron:
 TERM=screen-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.13.0-16-generic.efi.signed root=UUID=8c3a672d-6b6a-4ee4-b211-b148cc82e493 ro quiet splash vt.handoff=7
SourcePackage: x11-xserver-utils
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 08/06/2013
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: F5
dmi.board.asset.tag: To be filled by O.E.M.
dmi.board.name: 970A-D3P
dmi.board.vendor: Gigabyte Technology Co., Ltd.
dmi.board.version: x.x
dmi.chassis.asset.tag: To Be Filled By O.E.M.
dmi.chassis.type: 3
dmi.chassis.vendor: Gigabyte Technology Co., Ltd.
dmi.chassis.version: To Be Filled By O.E.M.
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrF5:bd08/06/2013:svnGigabyteTechnologyCo.,Ltd.:pnTobefilledbyO.E.M.:pvrTobefilledbyO.E.M.:rvnGigabyteTechnologyCo.,Ltd.:rn970A-D3P:rvrx.x:cvnGigabyteTechnologyCo.,Ltd.:ct3:cvrToBeFilledByO.E.M.:
dmi.product.family: To be filled by O.E.M.
dmi.product.name: To be filled by O.E.M.
dmi.product.version: To be filled by O.E.M.
dmi.sys.vendor: Gigabyte Technology Co., Ltd.
version.compiz: compiz N/A
version.libdrm2: libdrm2 2.4.83-1
version.libgl1-mesa-dri: libgl1-mesa-dri 17.2.2-0ubuntu1
version.libgl1-mesa-glx: libgl1-mesa-glx 17.2.2-0ubuntu1
version.xserver-xorg-core: xserver-xorg-core 2:1.19.5-0ubuntu1
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev N/A
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:7.10.0-1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20170309-0ubuntu1
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.15-2