This patch implements the new ways to get the project's hierarchy:
'subtree_as_ids': If True, returns projects IDs down the hierarchy
as a structured dictionay.
'parents_as_ids': If True, returns projects IDs up the hierarchy
as a structured dictionay.
Change-Id: Ia3afe994893dfca059cb8361f7ab1c14e28e1ad5
Implements: blueprint hierarchical-multitenancy-improvements