Separate Android Encryption Password from Lockscreen Password

This permits the use of a different (hopefully longer and more complex!) encryption
password, while using a simpler (and easier to type) lockscreen password.

Change-Id: Ia35fdcc769eee8fd7891678a532dafa0f4b3ba04
(cherry picked from commit d409060a9ca0ffb1382eb841ad54f176220fc8ab)