Minor Description
The SQLTransformer creates a temporary table when called, and does not delete this temporary table. When using a SQLTransformer in a long running Spark Streaming task, these temporary tables accumulate.
I believe that the fix would be as simple as calling `dataset.sparkSession.catalog.dropTempView(tableName)` in the last part of `transform`:
https://github.com/apache/spark/blob/v2.0.1/mllib/src/main/scala/org/apache/spark/ml/feature/SQLTransformer.scala#L65.
