Editing Keystone Services

Edited the document for clarity: addressed punctuation
points in the keystone services section, and also added edits
to clarify the Identity Concepts section. Moved Content from the
Keystone Services section to the Identity Concepts
Section.

Change-Id: I94d21ba16f89ea2ba12166bab3f6893091bccbbf
Implements: blueprint installation-guide-improvements
Merge "Editing Keystone Services"