Check for non-zero status code and hadoop client not found.

The fetcher would detect the condition where hadoop returns a success in
case of a success non zero value.

Review: https://reviews.apache.org/r/27670
Updated download instructions to latest version.

Changed the url and file name in `wget` and in `tar -zxf` commands
respectively.

This closes: #30
Review: https://github.com/apache/mesos/pull/30