Whether or not the v2.6 EXPERIMENTAL API is exposed at a site
depends on the enable_image_import config value. If it's False
(the default), then the API a client sees is the CURRENT v2.5
API, and any of the v2.6 calls made against 2.5 return a 404
(same as if you were running Ocata). This patch adjusts the
'versions' response so that when enable_image_import=False,
the EXPERIMENTAL v2.6 does not appear in the response.
Change-Id: Ibe164f02c99d10f5a5edd0de96c665413a12f700
Closes-bug: #1711829