cloud.install: Fix cloud packages on Debian

cloud-utils and cloud-initramfs-growroot are available in wheezy-backports.
No need to wget these packages.

https://packages.debian.org/wheezy-backports/cloud-utils
https://packages.debian.org/wheezy-backports/cloud-initramfs-growroot

Signed-off-by: Dimitri Savineau <dimitri.savineau@enovance.com>