NavBar: Slippery on the unsecured lock screen.

The NavBar is always non-slippery, except when:
 - the notification shade is showing
 - the 3 buttons (back,home,recents) are disabled

Also fix unrelated bug that ignored the "show panel delay"
before the first config change.

Bug: 6614842
Change-Id: Ib40adaef122b563809398fdebbd8a88d8f0c7ffd