[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`.
Sounds like a job for `HiveConf extends SQLConf`! After all, there's nothing better than confusing users trying to use `org.apache.hadoop.hive.conf`!