handle a backend disconnect gracefully

[missinglink]

Test what happens when the backend goes away and give an apologetic error to the consumer.

[missinglink]

If all the backend connections go away it handles it pretty gracefully, this is what I got in testing:

$ curl -vvv "http://localhost:3100/suggest?input=hack&lat=51.5&lon=0"
* Hostname was NOT found in DNS cache
*   Trying 127.0.0.1...
* Connected to localhost (127.0.0.1) port 3100 (#0)
> GET /suggest?input=hack&lat=51.5&lon=0 HTTP/1.1
> User-Agent: curl/7.35.0
> Host: localhost:3100
> Accept: */*
> 
< HTTP/1.1 500 Internal Server Error
< X-Powered-By: mapzen
< Charset: utf8
< Cache-Control: no-cache
* Server Pelias/0.0.0 is not blacklisted
< Server: Pelias/0.0.0
< Access-Control-Allow-Origin: *
< Access-Control-Allow-Methods: GET
< Access-Control-Allow-Headers: X-Requested-With,content-type
< Access-Control-Allow-Credentials: true
< Content-Type: application/json; charset=utf-8
< Content-Length: 45
< ETag: W/"2d-18f70f62"
< Date: Fri, 03 Oct 2014 13:48:18 GMT
< Connection: keep-alive
< 
* Connection #0 to host localhost left intact

{"error":{"message":"No Living connections"}}

happy with this, closing ticket