This patch adds role assignments list support
to keystoneclient.
Created RoleAssignment resource and RoleAssignmentManager
classes. RoleAssignmentManager only implements the list()
method, the other inherited methods from base.CrudManager
raises a MethodNotImplemented error with customized messages.
This bp is complimented with the OSC part:
https://blueprints.launchpad.net/python-openstackclient/+spec/roles-assignment-list
Change-Id: I164b58b67ff42320238e943ddfa9d0a8aadd0a6d
Implements: blueprint roles-assignment-support
Closes-Bug: #1246310