Refactorise Keystone resources management

Refactorise the code of Keystone resources management with backward
compatibility since we don't modify the unit tests except for the
"Require" that we replace by a Puppet ordering syntax.

Change-Id: Iebd35bd47d43733fdf2bc982936d49e531c62ea4
Implements: blueprint common-openstack-identity-resource
Merge "Refactorise Keystone resources management"