[Feature] Make etcd tuning flags to be configurable

[KesavanKing]

Feature (What you would like to be added):

As part of few performance tests on multi node etcd #107 we need the following flags to be configurable to arrive at the right tradeoff on initial bootstrap time of etcd nodes.

–heartbeat-interval –election-timeout –initial-election-tick-advance

Motivation (Why is this needed?):

Approach/Hint to the implement solution (optional):