Fix keyguard/Keystore storage issue

Keystore stored keys broke when keyguard was moved out of the system process
due to Keystore enforcing the calling app to be in the system process.

The fix moves the critical code into LockSettingsService, which continues
to live in the system process.

Fixes bug 10201270

Change-Id: I16e2de018e85b01265634dcfbefd7f06740dafa8