decouple API coverage report from main test suite target

... so that we can conditionally include the report only on
select branches of the build services configs

Bug: 77975055
Test: make -j cts dist                # no reports generated
      make -j cts-api-coverage dist   # reports generated

Change-Id: Iee812134f607e1e0580462e93dbc39268336bf4d
1 file changed