Add service groups config section

As noted in the bug report, we weren;t mentioning Zookeeper

This takes the writeup from
https://github.com/maoy/writeups/blob/master/ZooKeeperInNova.md
formats it in docbook, makes it a bit less dev-centric and formats it
so that future service group drivers can be added.

fixes bug 1106449

Patchset fixes missing xml:ids from new sections.

Change-Id: I7ec1a422e85a79489474e936c3a28816e74b30db
Merge "Add service groups config section"