IMPALA-1290: AnalyticEvalNode should have results ready after Open()

Change-Id: Id66defa1e7ff8a892a94aa8b754f2ea02d0af7c8
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/4450
Reviewed-by: Alex Behm <alex.behm@cloudera.com>
Tested-by: jenkins