Adding a custom property to the default VHAL impl

This property is supposed to be used mostly from e2e tests (a simple
test-case is provided in separate CL)

Test: make -j && runtest -x packages/services/Car/tests/vehiclehal_test/

Bug: b/36510399
Change-Id: I09b24f22ab328eee1ef6add60901ed03bf046874
4 files changed