MAPREDUCE-3035 and MAPREDUCE-3317
Now MRV2 job history contains hostName and rackName.
when rumen trace builder is ran on jobhistory, its generated trace contains hostname in form of
hostName : /raclname/hostname
But getHostName for LoggedTaskAttempt returns hostname as null
Seems that TraceBuilder is setting hostName properly but JobTraceReader is not able read it.