[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`.
When in doubt, make up longer names: `SQLConfigOpts`, `HiveConfigOpts`. But this is only possibly relevant in the future and should not block this PR.