Introduce PowerExemptionManager.

This is essentially identical to PowerWhitelistManager which will be
deprecated due to the use of non-inclusive language.

Bug: 180503057
Test: atest PowerExemptionTest
BYPASS_INCLUSIVE_LANGUAGE_REASON=Existing public API.
Change-Id: Ie6ff50118330e22b59a547c81952a31a5f5b54d8
4 files changed