Issue 858: Disable network configuration

This introduces two ways to skip network configuration changes usually performed by docker, as inspired by [issue 858](https://github.com/dotcloud/docker/issues/858):

* _docker run **-n=false**_ creates network-less containers

   Containers created with this option will only have a loopback interface. A given host can of course have both normal and network-less containers.

* _docker **-b none** -d_ completely disables network configuration in the docker daemon.
  
  This implies **-n=false** for every container, and also skips bridge creation & iptables operations. 

[Issue 858](https://github.com/dotcloud/docker/issues/858) is originally about disabling iptables, but I felt like these two levels of control made more sense - at least as a starting point. Maybe I'm missing something? Do we also need the ability to specifically disable iptables?

Note that there is currently no unit test for the "-b none" part of the branch - I'm waiting to see if the feature is interesting enough and confirm the approach is not completely backwards before figuring out how the test runtime stuff works (as it is a global daemon option, it looks like we'd need to run a separate test server).

This is my first docker pull request, so please let me know if I'm doing things wrong!