Formating Keystone Authentication Workflow diagram

Keystone Authentication Workflow diagram is distorted and difficult to read:

Move arrows away from text boxes
Fix distorted text boxes in Step 2

Change-Id: I9170e20cc26e23223508b8e4185e9c1fe2c685c6
Closes-bug: #1317106
Merge "Formating Keystone Authentication Workflow diagram"