Revert "Remove the packages::sssd_install_workaround, it was a hack"

This reverts commit 2404f682c71383c55adaf35c694ed16e727e6f26.

Conflicts:
	ltsp-build-client/puppet/ltsp/image/manifests/opinsys_desktop.pp

I guess we could need the "sssd_install_workaround" still for Precise.
Bring some wallpaper stuff to precise as well.