Add Memcached benchmark/performance driver for SBK

[kmgowda]

Describe the Issue (Bug/Feature) Add the SBK driver for Memcached performance benchmarking.

To Reproduce See the steps : https://github.com/kmgowda/SBK#add-your-driver-to-sbk to add the SBK driver for Memcached Get the know the Memcached IO APIs , start from here : https://github.com/memcached/memcached/wiki/Overview

Expected behavior SBK with -class Memcached and additional parameters should benchmark the Memcached storage performance

Additional context Understand the Memcached IO APIs and use them in the SBK template driver created using step: https://github.com/kmgowda/SBK#add-your-driver-to-sbk