SystemUI: hide navigation bar faster in SetupWizard

We use immersive mode in SetupWizard, and after bringing up the IME,
and in an external activity (i.e. Google account setup), the navigation
bar lingers around for 3000ms. This provides for a poor experience, so
let's hide it immediately if the device is not provisioned.

Change-Id: Id610ecddce75f1e21136db0d9a4160fe3d5e41bd
Signed-off-by: Roman Birg <roman@cyngn.com>