redis wrapper for twemproxy compat

refs CNVS-17062

This wrapper will catch any usage of the redis commands that twemproxy
doesn't support, including in specs, so that they don't sneak through.

test plan: specs should still pass, and redis caching should continue to
work as before.

Change-Id: I88d74c23c92c8be9f49e9399d8acbaf8ba31513e
Reviewed-on: https://gerrit.instructure.com/44710
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jacob Fugal <jacob@instructure.com>
QA-Review: August Thornton <august@instructure.com>
Product-Review: Brian Palmer <brianp@instructure.com>