Bug#743670: [jenkins.d.n] Hurd support on g-i-installation jobs

[Gabriele Giacone <1o5g4r8o@gmail.com>]

As said on irc, I can't reproduce black screen issue (see build #5 and
#6) on a wheezy chroot with patched qemu and you don't have time to do
some tests.

Could you please consider patches in my "experimenting" branch?

[hurd] Switch vga from cirrus to std to test whether black screen persists.
[hurd] vnc snapshot resolution to 1024x768, videobitrate to 1200.

"diskimage_poweroff" branch is also needed to power it off after disk
image test too, whenever we'll be able to install it.

Thanks,
-- 
G..e