[Pandora] More HFP tests

Implemented everything that I thought was feasible.

Missing tests either: (1) require in-band ringing to be disabled, (2) get stuck
in a loop setting codecs, (3) require us to configure the signal strength, (4)
require "speed dial", (5) require voice recognition, or (6) are flakey.

Bug: 237447510
Test: atest pts-bot:HFP

Change-Id: If5fc107271adb46be445da65222b23e5095b885c