update Images v2 API to include info about property protections

Updated image-update, image-list, and image-show calls to include
information about the possibility that the cloud provider may have
configured 'property protections', thereby affecting the user's
ability to create/read/update/delete properties.

Revised language in a non-redundant way to reflect the correct
audience for this document.

Change-Id: Ia1b9e2092e105e64199ce2f5d2a32ff7b2675d66
Closes-bug: #1236972
Merge "update Images v2 API to include info about property protections"