Add roles to all tempest created users

Adds configuration option identity.tempest_roles which is a list of
roles that are added to all tempest created users.

This is useful when tempest users require priviledges between default
and admin.

Change-Id: I545d8f595dad6e4fe3da57e936baf18bc16c0e78
Closes-Bug: #1411256
3 files changed