Keyguard should be dismissed if there is no trusted device.

The only times the keyguard is shown are:
1. To display unlock dialog when the initial user has a trusted device.
2. To display user switcher if the user clicks "Cancel" on the bouncer and
wants to switch to a different user.

Fixes: 140766764
Test: manual
Change-Id: I9e3c1138813ba40f0c6b2e8cba057b99ff6fb040