Print out content of VehiclePropValue when test fails

Currently when a test fails, it prints out a byte representation of the
object which is not helpful.

Bug: 277359330
Bug: 277359630
Bug: 277359374
Bug: 277359394
Bug: 277359419
Bug: 277359421
Bug: 277359396
Bug: 277359260

Test: atest FakeVehicleHardwareTest
Change-Id: I26c4260b2dbf5a71fbfe94e11c111b482337e6f5