First pass of haproxy load balancing

Simple implementation of single-node ssl-terminating non-ha load
balancing with haproxy. New variables:

- swift_haproxy_cert: cert to use for ssl endpoint. defaults to
                      snakeoil.pem, a self-signed cert. To use
                      another, concatinate into a giant-ass everything
                      .pem, copy it into roles/haproxy/files, and set
                      this variable to the basename of the file.

- swift_haproxy_stats_port: port to listen to the stats interface on
                            (defaults to 8000)

- swift_haproxy_stats_ip: what to bind to for the stats (default:
                          127.0.0.1)

- swift_haproxy_stats_username: username for stats page

- swift_haproxy_stats_password: password for stats page

In addition, another swift network has been defined ('proxy'), which
is the network that proxy realserver ips live.

Partial fix for #14