Add doc on glance property protection

In Havana, glance added a new feature: protection over
the properties on images. This adds a basic document
explaining it to the config reference.

Change-Id: Ifabc4d53f302c020bfcd87322d31a8d094a4abe8
Closes-Bug: 1217974
(cherry picked from commit a22972ef9f02c5f12c358a93283e892cab513514)
Add section on Keystone Token Binding

Havana added this feature, here are the docs.

Change-Id: I9c8c785f3eed91cc688f49e7dda7228cc1ff5216
Closes-Bug: 1196775
(cherry picked from commit 9d93c4f71f6f4f92ce7ac9c1e152d11de1fbde51)
Merge "Add section on Keystone Token Binding" into stable/havana
Merge "Add doc on glance property protection" into stable/havana