health AIDL: add vts tests

This is a direct translation of the health 2.0
and 2.1 VTS tests.

Some slight modifications are made (e.g. use googlemock
matchers) to make the test code more readable.

Test: run on Pixel
Bug: 203245778

Change-Id: Ifc3799a04a6a09d0d53f400b60d19fbfe004a3e3