Move Redis driver's claim transaction to Lua

This avoids having to set a watch and retry if someone else beats us to
the punch; the retry is less efficient than doing it with Lua, and would
require adding a backoff sleep to avoid lots of failed requests under
high concurrency.

This patch also adds a Redis server version check in the driver since
Lua requires redis-server >= 2.6

Change-Id: I0c34e267a6358965a54179a4b2fd03ac15b194e9
Closes-Bug: #1372510
Merge "Move Redis driver's claim transaction to Lua"