[Delivers #43559413 #43555603 #43555605 #43555607] Added User Agent header and new IdentityProvider tests

### Changes
- Updated to the latest __SimpleRestServices__ library
- Added the __User Agent__ HTTP header to all requests made to the Rackspace APIs.
- Added new __IdentityProvider__ tests:
    - __AddUser__ tests (with and without password specified)
    - __UpdateUser__ tests (updating username, email, enabled and default region)
    - __DeleteUser__