Fixes a Python3 syntax error

Python3 has a new way to raise an exception with an existing traceback.
In Python2 there was a special syntax, but that was removed in Python3.

bp python3

Change-Id: I6811f7f46693fc84d0c61116cdd4897b6c20a9fc
Example JSON files should be human-readable

Change-Id: I58a68829176a8447133c99908338b90b7204a694
implement GET /v3/catalog

Change-Id: I0ed53f4758cc6bd8771ef2b4b291480bbbfc1631
blueprint: get-catalog
Extracting get group roles for project logic to drivers.

get_group_project_roles is now implemented in each driver.

SQL and LDAP backends will see significant improvements on
performance (less queries made to resolve the groups).

KVS backend now supports inheritance and runs correct unit
tests.

Co-Authored-By: Pablo Fernando Cargnelutti <pablo.fernando.cargnelutti@intel.com>
Change-Id: I7a0190cd4a3b1eb26a09ef6436ca5450cf837135
Closes-Bug: #1205506
Merge "Extracting get group roles for project logic to drivers."
Merge "Fixes a Python3 syntax error"
Merge "Example JSON files should be human-readable"
Merge "implement GET /v3/catalog"