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
Merge "Clarified directives in Nova api-paste.ini"