Re-submitting OSSN 25 concerning Swift/Glance public images

Complete re-write adding more details.

Added section on root cause describing public label in Swift vs Glance,
as well as more details on fixes and their possible impacts.

Modified the config file and variable formatting per OSSN markup
standards, and smoothed over 'Summary' and 'Discussion' sections.

Expanded the 'delay_auth_decision' configuration item, clarified
remarks around auditing and configs, and specified this is in
multi-tenant mode only.

Split 'not use Swift' section into alternate back end storage section
and recommending Swift not in multi-tenant mode.

Change-Id: Ic61b2fa276a21e1617f90a3ce64f9e5972ff24bb
Closes-Bug: #1354512
Merge "Re-submitting OSSN 25 concerning Swift/Glance public images"