Added documentation and modified api-ref documents to
reflect multiple stores support changes.
Related to blueprint multi-store
Change-Id: I932297df8149968d31a5367a9ca71a5629045445
Generalizes the discussion to include the new web-download import
method and includes a new sample import request.
Change-Id: Icb6cd920f31c6e8e4eecf17880dd3244e5d1a61b
Closes-bug: #1748229
Adds documentation of the interoperable image import process
introduced in Pike in the EXPERIMENTAL Image API v2.6.
Change-Id: Ifbedc2e5e566db084bc7028ed4239485f0d68b18