remus::Client needs to handle a server that crashes

[robertmaynard]

As we start to hit more occurrences of faulty servers we need to make the client even more
reliable. This means that the client should have some polling abilities to allow us to detect a server
has failed, and to be able to return from a blocking call.

[robertmaynard]

The best way to handle this is to make the remus client follow the Lazy Pattern Approach ( http://zguide.zeromq.org/page:all#Client-Side-Reliability-Lazy-Pirate-Pattern )

We can get very simple reliable request-reply with some changes to the client.
We call this the Lazy Pirate pattern. Rather than doing a blocking receive, we:

- Poll the REQ socket and receive from it only when it's sure a reply has arrived.
- Resend a request, if no reply has arrived within a timeout period.
- Abandon the transaction if there is still no reply after several requests.