Change test type of flakiness dashboard uploads to match buildbot step name.

Flakiness dashboard assumed each buildbot step corresponds to one
test suite. So, it assumes the test type matches the buildbot
step name. This fix is somewhat hacky in that we won't be
able to make other test suites in mojob test upload to the
flakiness dashboard, but that's technical debt we already have
from smashing multiple test suites into one buildbot step.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/725993003