Refactor CountryDetectorService

Clean-up the test to use Mockito instead of the deprecated
AndroidTestCase, also getting rid of 1.5s of Thread.sleep.
No logic change.

Bug: 141626568
Test: atest CountryDetectorServiceTest
Merged-in: Ic0782b1ffcd1dcb30b9f1d91b37521d1f9887f03
Change-Id: Ic0782b1ffcd1dcb30b9f1d91b37521d1f9887f03
(cherry picked from commit 50361687ba6bc20877af43eb5367a5ba3a2911df)