API documentation for Hierarchical Multitenancy

Changes regarding the functionality of Hierarchical Multitenancy

- Changes in the Keystone API considering projects hierarchy.

Co-Authored-By: Rodrigo Duarte <rodrigods@lsd.ufcg.edu.br>
Depends On: blueprint hierarchical-multitenancy

Change-Id: Ieecb24c07e5e9d5e7215398244057a6d87501cfc
Merge "API documentation for Hierarchical Multitenancy"