UUID and HttpSM ID APIs and Machine support for a process UUID

As was discussed on https://github.com/apache/trafficserver/pull/199, I've started the work to generalize this, and breaking it up in various parts.

This first Jira is about adding four things:

1) An internal process UUID, which goes into Machine. It's accessible from the core.

2) An API to get this Machine UUID.

3) A set of generic UUID APIs, to do things like stringification, Copy() etc.

4) A very simple API that exposes the HttpSM's sequences number (sm_id).