Ensure export reports progress

If a hadoop task does not either write output or reports status for 10 minutes it is killed. Make sure we check back in periodically with hadoop to ensure it doesn't kill our export processes.

@brianhw @rocha
Do we have to use warn() for all info()-type log statements?  Seems like the wrong level, and would be better if we could fix output so that info stuff appears if that's what we want to see here.