[SPARK-2406][SQL] Initial support for using ParquetTableScan to read HiveMetaStore tables.

This PR adds an experimental flag `spark.sql.hive.convertMetastoreParquet` that when true causes the planner to detects table that use Hive's Parquet SerDe and instead plans them using Spark SQL's native `ParquetTableScan`.
I have mixed feelings about that.  The problem being that this only applies to HiveContexts, so it doesn't really make much sense in a SQLContext.