private boolean isTerminal(Operator<?> o) {
      return o instanceof FileSinkOperator || o instanceof ReduceSinkOperator;
    }
Temporarily truncates the operator tree to avoid full cloning of the tree.

It does the following simplifications:
<ul>
 <li> hides UNION operator parents which are unrelated to the current set of roots
 <li> hides childs from RS and FS operators
<ul>
ql/src/java/org/apache/hadoop/hive/ql/parse/GenTezUtils.java