Once system is provisioned, lock the screen on system user

If the device provisioning is complete, check if we need to show
the keyguard. We don't want it to show launcher after finishing
with setupwizard in the system user.

Bug: 25326078

Change-Id: I326069e29122ebf19a59fc00a9120cd5de70f231
diff --git a/core/java/android/provider/Settings.java b/core/java/android/provider/Settings.java
index 37f2c04..9034cc9 100644
--- a/core/java/android/provider/Settings.java
+++ b/core/java/android/provider/Settings.java
@@ -6285,7 +6285,10 @@
        public static final String DEVELOPMENT_SETTINGS_ENABLED = "development_settings_enabled";
 
        /**
-        * Whether the device has been provisioned (0 = false, 1 = true)
+        * Whether the device has been provisioned (0 = false, 1 = true).
+        * <p>On a multiuser device with a separate system user, the screen may be locked
+        * as soon as this is set to true and further activities cannot be launched on the
+        * system user unless they are marked to show over keyguard.
         */
        public static final String DEVICE_PROVISIONED = "device_provisioned";