Network API Rev 3

OK - this is revision 3 of the Network API. Thanks for all the feedback from everyone (rev 2 is at [tracker set 396](http://tracker.deltacloud.org/set/396). I'd like to consider committing these. Obviously they aren't finished. A change of this order undoubtedly brings lots of bugs and issues to be worked out (like required parameters for the create operations, i.e. defining the actual API). But I think the models are settled now - we are back to 3 resources: Network, Subnet, NetworkInterface. I believe fixes/changes can be made incrementally and the API will need to be documented as these changes are made. 

This patch set includes implementations for Mock (best place to start to understand how this all fits together), OpenStack, RHEV-M and EC2. The EC2 implementation is missing NetworkInterface (commented out in driver for now) as am waiting for the aws rubygem to include the NetworkInterface functionality (thanks [Tomas Sedovic](https://github.com/tomassedovic)). I also need to cut a release of the ruby-openstack rubygem to include the required [quantum functionality ](https://github.com/ruby-openstack/ruby-openstack/pull/23) (thanks [Ronelle Landy](https://github.com/rlandy) for the feedback).

I will put together some temp documentation on using this API - likely a blog post, that we can then copy into the Apache site docs once it all settles,

thanks, marios