Avoid polkit and bug

Accessing systemd/system with DBUS from
a user not root make systemd use polkit.
It doesn't work for us because:
 - at the end systemd crashes (sigsegv)
 - we don't want polkit here

Change-Id: I206edd108b8b659c8c6a3a68f61500cb114995d4
Signed-off-by: José Bollo <jose.bollo@iot.bzh>