testdrive does not support virtualbox 5

When using virtualbox 5 as virtualization software, testdrive-gtk cannot create new VMs anymore.

Looking at the code, the code basically says "only version 4.x is suppported", and fails otherwise.

The error in the UI is this:

"Error preparing virtualization: not enough arguments for format string"
The virtualbox version used is: 5.0.4-dfsg-2

The console output of the error is:

ERROR: not enough arguments for format string
Traceback (most recent call last):
  File "/usr/bin/testdrive-gtk", line 942, in prepare_to_launch_vm
    self.ovirt.validate_virt()
  File "/usr/lib/python2.7/dist-packages/testdrive/virt/virtualbox.py", line 73, in validate_virt
    "please install v4.0 or newer.") % self.vboxversion
TypeError: not enough arguments for format string
ERROR:testdrive-gtk:not enough arguments for format string
Traceback (most recent call last):
  File "/usr/bin/testdrive-gtk", line 942, in prepare_to_launch_vm
    self.ovirt.validate_virt()
  File "/usr/lib/python2.7/dist-packages/testdrive/virt/virtualbox.py", line 73, in validate_virt
    "please install v4.0 or newer.") % self.vboxversion
TypeError: not enough arguments for format string

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: testdrive-gtk 3.27-0ubuntu1
Uname: Linux 4.2.0-040200rc7-generic x86_64
ApportVersion: 2.18.1-0ubuntu1
Architecture: amd64
CurrentDesktop: XFCE
Date: Sun Sep 13 18:00:21 2015
InstallationDate: Installed on 2015-02-05 (219 days ago)
InstallationMedia: Xubuntu 15.04 "Vivid Vervet" - Alpha amd64 (20150205)
PackageArchitecture: all
SourcePackage: testdrive
UpgradeStatus: Upgraded to wily on 2015-05-28 (107 days ago)