Fix ActivityRecordTests.

Tests are not guaranteed to run on the same thread as setup methods.
Therefore, we must ensure any loopers used are already created by the
time the test runs. We do this now by creating a HandlerThread and
referencing its Looper later. Loopers are initialized per
HandlerThread, which will allow us to both isolate its usage and
guarantee the Looper initialization by test time.

Change-Id: If15494783959e5c399375033253cef69b921ff84
Fixes: 36916522
Test: bit FrameworksServicesTests:com.android.server.am.ActivityRecordTests