[SPARK-20548] Disable ReplSuite.newProductSeqEncoder with REPL defined class

## What changes were proposed in this pull request?

`newProductSeqEncoder with REPL defined class` in `ReplSuite` has been failing in-deterministically : https://spark-tests.appspot.com/failed-tests over the last few days. Disabling the test until a fix is in place.

https://spark.test.databricks.com/job/spark-master-test-sbt-hadoop-2.7/176/testReport/junit/org.apache.spark.repl/ReplSuite/newProductSeqEncoder_with_REPL_defined_class/history/

## How was this patch tested?

N/A

Author: Sameer Agarwal <sameerag@cs.berkeley.edu>

Closes #17823 from sameeragarwal/disable-test.