config-ref: include keystone tables

Include keystone configuration options in the Identity section.

There is room for lots of improvements, but this first step will at
least make the info available.

Replace "Identity Service" with "Identity service" in the config-ref.

Closes-Bug: #1277330
Change-Id: I2dfac169c89bdbecd67322923a6a84f2155c4150
Merge "config-ref: include keystone tables"