In case 'data' image attribute is a base string (instead of in-memory
or on-disk file), api.glance sends back an image wrapper with a redirect
url and a token to its caller, so the caller could upload the file to
that url directly.
Provide a unit test for api.glance behavior when an external upload
location is used. That also requires to fix glance stub endpoint data
in keystone_data.py since it didn't reflect the reality.
Also document the new HORIZON_IMAGES_UPLOAD_MODE setting that will
govern direct images upload and the define approach to deprecating the
old HORIZON_IMAGES_ALLOW_UPLOAD setting. The old setting is deprecated
as of Newton release and planned to be removed in P. 'Removing' means
that it will no longer be used / referenced at all in code, not the
actual presence in settings.py (it is removed from settings.py in this
commit). What really matters is if the customized value of
HORIZON_IMAGES_ALLOW_UPLOAD in local_settings.py will be still
considered during the deprecation period.
Help text in Django Create Image form in case if local file upload was
enabled was wrong, fixed that.
Related-Bug: #1403129
Partially implements blueprint: horizon-glance-large-image-upload
Change-Id: I24ff55e0135514fae89c20175cf9c764e871969b
7e65af5f13