exclude pending tests from coverage data

Our coverage numbers were slightly inflated by some pending tests (especially Planner tests). This change causes the pending tests to become `skipped` when Travis runs the coverage. When run normally, they are still pending (and still will fail if their assertions start succeeding).

This reduces our overall coverage by about 1% (to just below 58%). Per @sellout, I'm killing the previous PR that increased our required coverage to 58%.