Add --logtostderr when running tests so we get full logs when things fail.

Test Plan: make test

Reviewers: andybons, jiangmingyang, spencerkimball

Reviewed By: andybons, jiangmingyang, spencerkimball

Subscribers: jiangmingyang, andybons, team

Differential Revision: http://phabricator.cockroachdb.org/D109