Fix: BroadcastradioHalTest.DabTune case failure

Root Cause: Even when proper DAB signals are available, the test-case
"BroadcastradioHalTest.DabTune" always fails. This is because the Pro
-gramSelector created as part of the test-case is not valid according
to the AOSP documentation; it passes only DAB_FREQUENCY as the Primar
-yId, but according to the AOSP documentation, DAB_FREQUENCY is not p
-art of proper acceptable PrimaryIds in a ProgramSelector

Fix: The test-case is modified to retrieve the station list before pe
-rforming any tune in the test-case; there are three possible outcome
-s:
- If there are no stations in the station list, the test-case shall b
  -e skipped
- If there are stations in the station list, but there are no dab sta
  -ions being transmitted/received, the test-case shall be skipped
- If there are stations in the station list, and if there are DAB ser
  -vices, extract one service from the list, and create a ProgramSele
  -ctor, and send a tune-request

Test: run "VtsHalBroadcastradioV2_0TargetTest from VTS; run the test-
case - "BroadcastradioHalTest.DabTune"

Bug: 208477956
Change-Id: I874d36f9eeb460fabadd06fe1e138a35b13a5816