Adding RunIn to run a user specified command in an existing container.

This is aimed at providing RunIn support in docker. I don't personally like the API as-is since it requires the users to provide container specific information which is already checkpointed. In the future, the API will evolve to just require the container ID and derive the config and state based on it. 
All this code here does not work correctly because it's being applyed to the first exec and causing issues with chars and the terminal for the containers initial process