Add libweave's unit tests to autotest

Renamed the test binary to libweave_test to stay consistent with
other Brillo test runner and marked it to be executed as part of
brillo_Gtests test.

BUG: 25672600
Change-Id: If8d5c9228ac67e535d95a3efabb4c1ecd2763683
Reviewed-on: https://weave-review.googlesource.com/1521
Reviewed-by: Vitaly Buka <vitalybuka@google.com>