Making HadoopPipeline.submit return Tool status

This submit method is a thin wrapper around ToolRunner.run.
ToolRunner.run returns the integer exit status produced by the Tool
implementation it executes.  Prior to this commit, submit returned
void and threw the status away.  Now the status is returned from
submit.  This change is groundwork for a new integration test method
related to #806 and #826 that will submit a HadoopPipeline that
submits a typical graphson-to-sequencefile dump job and needs to know
whether the job succeeded.
Adding a test single-map/no-reduce job

This test will detect a regression on #806 / #826.  I checked that it
failed when I locally reverted
520e7c650e08ebc2d6b86bfa1515f032006259f4 (the commit that fixed this
bug in manual testing).
Improve Hadoop job output dir log message

The output dir for each individual job is now logged at DEBUG, instead
of logging a string prefix common to all jobs that wasn't actually a
directory or file by itself.