Updates to Terasort (no functional change)

1. Set default value to Terasort XML file
2. Remove "StrictHostKeyChecking=no" from ssh/scp commands as Hadoop
uses SSH to control the Hadoop related processes on the slaves.  If
StrictHostKeyChecking is not disabled in the SSH config files, Hadoop
will fail.  The error returned by SCP is much easier to troubleshoot
than the error Hadoop reports if it cannot control a slave.