extend JobClient.runJob(JobConf) with the ability to take a timeout, so fail better during test runs

Tests that submit jobs via JobClient hang until they are killed if something goes wrong in the back end -JobClient does not impose limits on how long runs should take, but JUnit does. If we had an overload of runJob() that took a timeout, JobClient could kill a job that was taking too long, extracting the stack trace and better diagnostics to the test reports.