Clarified directives in Nova api-paste.ini

Clarified directives in Nova api-paste.ini for controller and compute
nodes based on a working configuration.  Also cleaned up some
formatting issues.

Change-Id: I60408caff40934de85502b845627ddb2ebe83a27
Closes-Bug: #1248001
(cherry picked from commit 56ef4d3085f6be34c0e1bb0a2b62f18bcc9f562f)
Merge "Clarified directives in Nova api-paste.ini" into stable/havana