The only change from the Pike version is that I've added wording that
the call to `GET /allocation_candidates` will also need to be modified
to include the root filter. I've also updated the History section.
Previously-approved: Ocata
Previously-approved: Pike
Blueprint: nested-resource-providers
Change-Id: I6b5531a0fe8c1aa5056d25ae47901b05e241eb9e
5648432cda