do-release-upgrade -s crashes on 15.10

[Maxime Ménard-Leroux]

When launching 'do-release-upgrade -s', it crashes when creating the sandbox.

$ lsb_release -rd
Description: Ubuntu 15.10
Release: 15.10

$ apt-cache policy ubuntu-release-upgrader-core
ubuntu-release-upgrader-core:
  Installed: 1:15.10.14.4
  Candidate: 1:15.10.14.4
  Version table:
 *** 1:15.10.14.4 0
        500 http://ca.archive.ubuntu.com/ubuntu/ wily-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     1:15.10.13 0
        500 http://ca.archive.ubuntu.com/ubuntu/ wily/main amd64 Packages

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: ubuntu-release-upgrader-core 1:15.10.14.4
ProcVersionSignature: Ubuntu 4.2.0-35.40-generic 4.2.8-ckt5
Uname: Linux 4.2.0-35-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.19.1-0ubuntu5
Architecture: amd64
CrashDB: ubuntu
Date: Thu Apr 21 18:28:43 2016
InstallationDate: Installed on 2015-10-07 (197 days ago)
InstallationMedia: Ubuntu 15.10 "Wily Werewolf" - Alpha amd64 (20150924)
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=en_CA:en
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_CA.UTF-8
 SHELL=/bin/bash
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to wily on 2016-04-21 (0 days ago)