WIP: tighten identifier spec 

DO NOT MERGE YET

There are still a couple open questions.  As I read through it I wanted to wordsmith a bit, which lead to reordering some to read sort of top-down.  There were a couple things I thought were wrong (pod name should be a subdomain) and a few things I think we can make more concise.  I also added examples and clarifies corollaries.

@smarterclayton in particular


If we assert that namespace.name is unique, then we can start the container as name_namespace and we can always find it later.  I guess the problem comes if we terminate that container, but have not removed it yet, and another request comes in for the same name.  Docker barfs on that, so we do need a unique ID in there.  OK, I am sold.