Host test script should return 1 when build fails or test is missing

* test/run_host_unit_tests.py returns 1 when
  - Build environement could not be setup
  - Build fails
  - Test could not be found
* It returns 0 when
  - Test exists, but failed
  - All tests pass

Bug: 64687730
Test: ./test/run_host_unit_tests.py -j40
Change-Id: Idbff0c73a219b5ce7b640f44f41caf43030e2b51