updated documentation, default.xml, job submission fix

The rename that happened in HCATALOG-549 did not have corresponding doc update.
The webhcat-default.xml needs to have better defaults.
The mapreduce.job.credentials.binary in job submission is needed for secure job submission, but since the secure mode job submission changes are not part of 0.5 changes, it makes sense to remove it. It actually causes failure in non pig job submission.