Added additional error checking around the mullti-threaded mkfs.ext4 call.
This protects against mounting HDFS file systems which do not format
correctly due to hard disk formatting failures.
Capture the formatting PID's and process return codes for each
thread driven disk formatting call and mark the disk as non-mountable if
the call fails. See pid = ::Process.fork & ::Process.waitall
for details.
Merge pull request #83 from Paul-Webster/pull-req-release-fred-master-93dfded8a80f8417afd9ca6bb1143ce840388ff9

Added additional error checking around the mullti-threaded mkfs.ext4 call [1/1]