This PR is a complete rewrite of sind

Fixes #39 #38 #37 #35

Features & Usage improvements

• sind now only relies on the docker host and no longer on a config file
• sind can now start and stop the clusters, avoiding to recreate them.
• IP of containers are now fixed, to enable start and stop
• sind inspect enables to inspect the current state of a cluster
• sind push gets a new --file option enabling to push an already existing file generated by docker save
• sind ls output is updated and displays node stats

Code

• Faster integration suite, as most of the testing details has been moved to an unit test suite mostly on the pkg/sind/internal package.
• API has been broken, to enable users to inject their own docker client instance.

TODO

• Backport and test sind ls
• Backport sind push and support the --file option
• Impement sind inspect
• Bonus: support a --tmpfs flag on sind create for faster io on nodes.