Please try first whether the host is reachable at all. This can easily be done using nmap. For your case this should suffice:
nmap localhost -p 22
If it says that the port is open, you should look into the sshd on the guest. If it is filtered, maybe a firewall-issue on your guest (incoming) or your host (outgoing/incoming from local).
On the update:
Simply put, you have two choices:
Use bridged networking for example as described in here, that way you can install the sshd.
Use guestfwd. As you already established a connection (port forwarding) via qemu in one direction, you can easily do the same the other way around:
- Install a proxy on your host (squid, tinyproxy, whatever)
- Point the guest to your proxy: (below untested part of your command):
guestfwd=tcp::3128-:3128
- Last, but not least: Use http_proxy for the apt commands or set the variable system-wide.
When you finally have the sshd running, you should be able to connect to the guest system via ssh.