wheezy: adapt persistence of NM connections

Persistence for NM connections is broken. See corresponding issue in Liberte

Is it really, even after most of the secrets handling was moved back to GNOME keyring, and the Wi-Fi connections back to be considered as "user" ones unless user is allowed to configure system ones (since network-manager-gnome 0.9.4.1-3)? Perhaps tweaking the policykit settings so that the amnesia user is not allowed to configure connections would be enough to workaround this?

Parent Task: #6015 (closed)

Original created by @tails on 5367 (Redmine)