O'Reilly: user-facing technical comments

This commit addresses the technical comments from O'Reilly for the
user-facing chapter. The instance data section has been
reorganized for clarify. The block volume attachment has been
edited for correctness and clarity as well.

Change-Id: I564101b8cd2d8d4204c594baba28bffc78ed0dd6
Merge "O'Reilly: user-facing technical comments"