Adding filesystem stats to db storage drivers. 

Moved 'FsStats' to 'info' package to make it easy for users.
We don't push the Spec as of now. If we start doing that, then we can move capacity to the Spec table and just add usage here. I think we need to push the Spec somewhere. CPU and Memory limits should also be pushed. I will work on that sometime soon. For now, I prefer to leave it as-is.