Add support for HS2 protocol V6

This patch adds support for V6 of the HS2 protocol, which notably
includes columnar organisation of result sets. Clients that set their
protocol version to < V6 will receive result sets in the traditional row
orientation.

The performance of fetches over HS2 goes up significantly as a result,
since the V1 protocol had some pathologies in its deserialisation
performance.

 Beeswax
  Row materialisation: 455ms, client processing time: 523ms
 HS2 V6:
  Row materialisation: 444ms, client processing time: 1.8s
 HS2 V1:
  Row materialisation: 585ms, client processing time: 15.9s (!)

TODO: Add support for the CHAR datatype

The following patch is also included:

Fix wait-for-hiveserver2.py when Impala moves to HS2 V6

Due to HIVE-6050, older versions of Hive are not compatible with newer
clients (even those that try to use old protocol
versions). wait-for-hiveserver2.py uses HS2 to talk to the HiveServer2
service, but picks up the newer version from V6, and fails.

This patch temporarily re-adds cli_service.thrift (renaming the Thrift
service as LegacyTCLIService) only for wait-for-hiveserver2.py to
use. As soon as Impala's thirdparty Hive moves to HS2 V6, we can get rid
of this change.

Change-Id: Ifffa9c2f14ddf0b039588ec3ba880b03a98446e2
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/4195
Tested-by: jenkins
Reviewed-by: Henry Robinson <henry@cloudera.com>