haproxy: Initial support

Start OSv by:

$ sudo ./scripts/run.py  -nv

On Host:

$ ssh 192.168.122.89
$ links http://192.168.122.89

Note:
By default, traffic to guest(192.168.122.89) port 80(http) and 22(ssh) are
routed to host(192.168.122.1) port 80 and 22. See haproxy.cfg.

Signed-off-by: Asias He <asias@cloudius-systems.com>