Idv3 updates

[auhlig]

This PR introduces

• little refactoring of integration tests to make it easier to use
• updated howto-readme along the way
• get service catalog - http://developer.openstack.org/api-ref/identity/v3/index.html#get-service-catalog
• get project scopes - http://developer.openstack.org/api-ref/identity/v3/index.html#get-available-project-scopes
• get available domain scopes - http://developer.openstack.org/api-ref/identity/v3/index.html#get-available-domain-scopes
  The 3 new method come with tests.

Let me know what you think @vinodborole

[vinodborole]

Awesome stuff @auhlig LGTM 👍

[auhlig]

Cool. Thanks @vinodborole