Add configuration guide sections for more required options

This commit adds additional sections to the tempest configuration guide
to elaborate on the details of several required options when configuring
tempest. Specifically this covers how to set the keystone connection
info, flavors to use for testing, and image setup.

Change-Id: I5a72443a3b05e39eba2eac1c4c9a4d6eef26797d
1 file changed