Specify -p explicitly for Docker 0.6.5+ security changes. Also create .znc folder in prereqs.

As per [this blog post](http://blog.docker.io/2013/10/docker-0-6-5-links-container-naming-advanced-port-redirects-host-integration/), Docker has recently updated Docker so that you need to pass `-p <port>` with `docker run` in order to expose ports now.

```
First, we are changing the default behavior of docker run to not redirect ports 
on the host. This is better for  security: ports are private by default, and you 
can explicitely publish them with the -p flag. If you currently rely on exposed 
ports being published on all host interfaces by default, that will no longer be 
true in 0.6.5. You can revert to the old behavior by simply adding the 
appropriate -p flags.
```