Authenticate correct user's account when pattern fails multiple times.

Bug: 7473142

Provide hidden methods in AccountManager for querying accounts and
authenticating for a specific user. Lockscreen is running in the
system process. Allow only system process to access accounts across
users.

Also make sure to launch the lock settings screen on the just reset
user using startActivityAsUser()

Change-Id: Ifefc0039ba2b51396b8bd0268f36d5271a3d8676