redis input piplined and eval batched requests support

Added :batch_size option for doing a batched lpop by EVAL lua script
and :pipeline_size option for pipelining , in case  :batch_size > 1 each pipelined request will use EVAL

EVAL makes sense over PIPELINE in bursty traffic workload
and in tests some combinations of EVAL + PIPELINE showed a bit better performance than
just EVAL or just PIPELINE