Add list roles api to identity v3

Identity v3 lack of list roles, so I do the addition.
To test the addition, I add a test in :
- test_role_create_update_get
and rename it :
- test_role_create_update_get_list

Change-Id: I1163df683ad16643773b3c75d895296c7e601b6b
Merge "Add list roles api to identity v3"