VTS: Add vts-core to the dependency of tests

Bug: 137921421
Test: (1) m tests
      (2) check vts-core-tests.zip

For migrating most existing VTS test to executable by Base TradeFed, we have to
create vts-core suite and test all of the modules in vts-core first.
And add the packaging rules for vts-core suite.

Bug: 137921421
Change-Id: Ifc92db205c78db98abf704aa6dfa50f1f77e983d