Taking screenshots on xenial host fails.

[Lyn Perrine]

To reproduce install virt-manager on a xenial install and boot a guest with kvm/qemu x86 backend I have not tried to reproduce with all the others yet. Install a guest and when running an GUI click virtual machine -> take screenshot on the guest in the menu. I get the error message

Error taking screenshot: argument 1 must be convertible to a buffer, not _ResultTuple

Traceback (most recent call last):
  File "/usr/share/virt-manager/virtManager/details.py", line 1455, in control_vm_screenshot
    return self._take_screenshot()
  File "/usr/share/virt-manager/virtManager/details.py", line 1507, in _take_screenshot
    file(filename, "wb").write(ret)
TypeError: argument 1 must be convertible to a buffer, not _ResultTuple

Which seems to be a type error in python. virt-manager:
  Installed: 1:1.3.2-3ubuntu1
  Candidate: 1:1.3.2-3ubuntu1
  Version table:
 *** 1:1.3.2-3ubuntu1 500
        500 http://us.archive.ubuntu.com/ubuntu xenial/universe amd64 Packages
        500 http://us.archive.ubuntu.com/ubuntu xenial/universe i386 Packages
        100 /var/lib/dpkg/status

Description: Ubuntu 16.04 LTS
Release: 16.04

I expected clicking to save a screenshot would save an image file on my computer. Instead I get a popup warning message and an empty image file that does not open in any image viewer.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: virt-manager 1:1.3.2-3ubuntu1
ProcVersionSignature: Ubuntu 4.4.0-22.40-generic 4.4.8
Uname: Linux 4.4.0-22-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia_modeset nvidia
ApportVersion: 2.20.1-0ubuntu2
Architecture: amd64
CurrentDesktop: LXDE
Date: Fri May 20 13:50:26 2016
InstallationDate: Installed on 2015-09-20 (242 days ago)
InstallationMedia: Lubuntu 15.10 "Wily Werewolf" - Alpha amd64 (20150920)
PackageArchitecture: all
SourcePackage: virt-manager
UpgradeStatus: Upgraded to xenial on 2016-03-12 (68 days ago)