Adds automatic switching to Guest if user starts driving with the keyguard

up.

driving_on_keyguard_timeout_ms controlls the number of milliseconds we wait,
before switching to Guest. If this number is negative, feature is disabled.

Change-Id: Ic1357362a97cb14a4f221d53e17a30cd3fefc5ea
Fixes: 110228676
Test: manual testing on mojave and emulator. Toggling driving state and keyguard, and observing the timer logs and switching.