Ability to fan out to all peers and return results

[prashantv]

When using -P, a single request will randomly select a peer, while benchmarking will round-robin between peers.

It would be nice to support some sort of a --fanout option to fanout a request to all peers. E.g.,

$ yab -p 1.1.1.1:1 -p 2.2.2.2:2 moe --health
1.1.1.1:1
[ health output]
2.2.2.2:2
[ health output ]

Benchmarking with --fanout should benchmark each individual host:port individually and return results so we can easily determine which instance is slower.

cc: @nomis52