Set upload_image policy to control data upload

There was no policy to control data upload.
Up until today, the add_image policy was a all or nothing, from metadata
to the actual data. Now, with the combination of add_image and upload_image
an administrator will have finer control over the whole chain.

Change-Id: I1a7966ffb5c63dd8239a54fe2963b031d9fe1f9a
Closes-bug: #1254521
Add documentation for some API parameters

Add documentation for some parameters which can
be present in glance-api.conf:

* use_user_token
* admin_user
* admin_password
* admin_tenant_name
* auth_url
* auth_region
* auth_strategy

Fix for bug 1256952.

DocImpact

Change-Id: Ia5b731cabaec961f3a4226d30abd3bca9bd87651
Merge "Set upload_image policy to control data upload"
Merge "Add documentation for some API parameters"