BrandedAccountPreferenceControllerTest converted to JUnit

Resource determining controller availability is mocked, rather than
using robolectric device config.

Diff: https://diff.googleplex.com/#key=JywCGq1rz3Pb
Test: atest -c BrandedAccountPreferenceControllerTest
Change-Id: I14e6db63af29479cb663895f9d9259bff0df43b7