Glide should sort subpackages alphabetically to avoid spurious diffs

[technosophos]

I've noticed that the re-arrangement of subpackages: sections introduces changes to the lock file that are more just clutter than anything else. On a recent update of Kubernetes, I spent quite a bit of time just tracking movements inside of the lock file.

It seems to me that we could just sort subpackages lexicographically, and that would lead to predictable ordering. The easiest way to do this would be in a marshaling hook in the cfg/lock.go and cfg/conf.go files.