[hive] Go back to using the getTables API instead of executing SHOW TABLES commands (for HS2)

Hive HiveServer2 has a compile lock which serializes all query compilation. Hue was updated to use "SHOW TABLES" in HUE-2243 due to slowness in the Hive getTables() API. This is bad because it means the SHOW TABLES commands will be serialized, potentially behind a query that is expensive to compile (very complex or queries a larger number of partitions). This leads to inconsistent performance in Hue metadata browsing.

In HIVE-7575 the performance issues in the Hive getTables command is being resolved. Hue should update to go back to using this API once the change is available in Hive. Impala may need to continue to use SHOW TABLES until it improves performance of getTables() as well.