Implement etcd client for original ycsb

[jeffa5]

Is your feature request related to a problem? Please describe.

go-ycsb is a good solution to get us going but the original ycsb would be better for cross-analysing systems from other works. We would just need to implement a new database driver for etcd to cover both etcd and lskv.

Describe the solution you'd like

A new client driver for ycsb that can talk to etcd.

Describe alternatives you've considered

go-ycsb but it isn't as featureful.

[jeffa5]

https://github.com/etcd-io/jetcd should be useful, though it is work in progress but official