bug#22053: silent failure on guix environment foo --container

[Efraim Flashner <efraim@flashner.co.il>]

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When trying to run `guix environment foo --container` I don't get a container
with a new shell or any useful information, it just thinks about it for a
while and then returns to the command prompt, allowing me to enter another
command.

efraim@debian-netbook:~$ strace -f -o log guix environment vim --container ; echo $?
1

efraim@debian-netbook:~$ uname -a
Linux debian-netbook 4.3-0.dmz.2-liquorix-amd64 #1 ZEN SMP PREEMPT Debian 4.3-2 (2015-11-17) x86_64 GNU/Linux

efraim@debian-netbook:~$ sudo sysctl -w kernel.unprivileged_userns_clone=1
sysctl: cannot stat /proc/sys/kernel/unprivileged_userns_clone: No such file or directory
(this kernel does allow running VMs as user, which makes it nice)

efraim@debian-netbook:~$ guix --version
guix (GNU Guix) 0.9.0

-- 
Efraim Flashner   <efraim@flashner.co.il>   אפרים פלשנר
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