service: Enable all tests for target

Made some changes to the test structure following the instructions
at http://go/brillo/brillo-team/testing:

  - Renamed the existing host and target tests to bluetoothtbd-host_test
    and bluetoothtbd_test respectively.
  - The target suite now includes ALL daemon unit tests + binder tests.
  - Added custom test/main.cpp to set up logging and command-line. Now
    we can run tests with the -v flag to increase log verbosity level.

Bug: 24708686
Change-Id: Ia4ce5d7028ce6cb0efd4a1c51ffebdf3bbe6921e