Snapshot fails if process can't write to /tmp

[dkincaid]

Since "/tmp/filecopy" is hardcoded in FileCopyInputFormat as tmproot if a snapshot is run and the user running the process isn't able to write to "/tmp" or "/tmp/filecopy" the snapshot will fail. Should this use the config property "hadoop.tmp.dir" instead?

[sorenmacbeth]

Sure, that sounds reasonable. I'd be happy to accept a PR for this.