GNS3 Docker support pending merge

So the experimental GNS3 support for Docker is done. I'm sure that it has a few bugs but that's why it's experimental. We're discussing what to do with the code, either merge them from their respective docker branches to unstable or ship it with the latest version of GNS3. Because I like to keep users in the loop here's the transcript of our discussion:

We have two options:
* wait that the unstable branch become the master branch at the 1.4 release and move docker branch as the new unstable branch
* merge docker support to unstable and add in settings an experimental flags to show this option.


I've synced the unstable branch with docker branch sometime last week so if nothing major has been going on in the last couple of days it should be mergeable.
We should do two things.
Basically, importing docker branch to master branch shouldn't cause any problems with the rest of the code IF GNS3 successfully runs on those machines. Please note that I haven't tested it on Windows or Mac since Docker support in those operating systems has different setups and I'm not sure how docker-py will behave on those systems. Docker-py attaches to a socket on Linux so my priority was to do it on Linux. As long as GNS3 starts and you can work with other VMs you should be fine. If there's an error it should be easily fixable with an if statement or similar so let me know if this happens, I'd be glad to fix issues and improve Docker support after GSOC. Once we're sure the rest of the code is OK we're good to merge even if Docker support isn't extensively tested. 

That being said, I'm not sure what your policy is on users getting errors but I'm all for pushing new code as soon as possible as long as it's flagged experimental so users are aware that it might crash and can't crash the rest of the product. This way users will start using/testing it for us and report bugs without getting frustrated. I'd say DO IT! :D

Feel free to try it before it gets polished and merged in to GNS3 master branch. Install the latest versions of GNS3 server and GUI from the docker branches:

• https://github.com/GNS3/gns3-server
• https://github.com/GNS3/gns3-gui

Make sure the user running GNS3 has permissions to create and manipulate Docker containers. This is usually accomplished by adding that user to the docker group and the popular Linux distributions *should* do the rest but check the Docker documentation on how to run Docker without root permissions.

Also, Docker support requires ubridge to manipulate network namespaces and do UDP tunnels. Use the latest version from master branch:

• https://github.com/GNS3/ubridge

It's a cool little project in by itself and has some interesting features.

I'll write something more detailed on how to use this new Docker support but until then - try it yourselves!