Properly handle replica count > 1.
Properly handle replica count > 1.

We were generating invalid chains in the map before because we weren't
prohibiting hosts farther back in the chain from being assigned later
in the chain.

Change-Id: Ia6bd6f68905f2b99b0e4b4a4fd5823b6c4f58ffe
Reviewed-on: http://review.northscale.com/1925
Reviewed-by: Steve Yen <ef850f73f7832052d3c6d9b5ddd3a1716d9a57f1@gmail.com>
Tested-by: Steve Yen <ef850f73f7832052d3c6d9b5ddd3a1716d9a57f1@gmail.com>

mschoch/ns_server,mschoch/ns_server,ceejatec/ns_server,nimishzynga/ns_server,nimishzynga/ns_server,nimishzynga/ns_server,mschoch/ns_server,ceejatec/ns_server,pavel-blagodov/ns_server,pavel-blagodov/ns_server,t3rm1n4l/ns_server,mschoch/ns_server,ceejatec/ns_server,nimishzynga/ns_server,daverigby/ns_server,pavel-blagodov/ns_server,membase/ns_server,ceejatec/ns_server,vzasade/ns_server,t3rm1n4l/ns_server,t3rm1n4l/ns_server,ceejatec/ns_server,nimishzynga/ns_server,mschoch/ns_server,mschoch/ns_server,t3rm1n4l/ns_server,daverigby/ns_server,membase/ns_server,membase/ns_server,pavel-blagodov/ns_server,ceejatec/ns_server,vzasade/ns_server,membase/ns_server,daverigby/ns_server,daverigby/ns_server,daverigby/ns_server,vzasade/ns_server,membase/ns_server,vzasade/ns_server,nimishzynga/ns_server,t3rm1n4l/ns_server,membase/ns_server