Documentation for using policies for protected properties

Add documentation for using policies to describe
property protections.

Related to bp api-v2-property-protection

Change-Id: Ic1fc4d3d69dee7ba65462a5bda6cdbe1a266077e
Remove lxml requirement

Fixes bug 1252344

Change-Id: Iaa10b7c78bf03b00c84a27592265bb79203df376
Adding an image status transition diagram for dev doc

Now there is no image status transition diagram in the dev
doc, this patch will add one and keep the image source as
a dot file so that it can be updated easily in the future.
See http://www.graphviz.org to get more info about .dot file.

Fixes bug 1244995

Change-Id: I076c461f688be93eab8d3d1fa541990d7b79da5e
Add upload policy for glance v2 api

Related to bug 1250918

There currently exists no check in set_data function for glance
api v2 in the policy layer. This patch adds upload_image policy.

DocImpact

Change-Id: Ibccc78f8bccff3baa5aca574cf17bd14c5403ca2
Merge "Add upload policy for glance v2 api"
Merge "Adding an image status transition diagram for dev doc"
Merge "Remove lxml requirement"
Merge "Documentation for using policies for protected properties"