Introduce logout button and DevicePolicyManager API to enable it

Bug: 67843538
Test: Manual test with CloudDpc that logout button can be controlled by DevicePolicyManager API and only enabled in shared userse
Test: Logout button can actually exit the user and ActivityManager log shows that user is stopped
Test: CTS is tracked in b/67843605
Change-Id: I9f27050654958ce55f574dd05ff80609255ffeb4
9 files changed