[Delivers #43555597 #43555601] Added Tests for Identity Service: Authenticate, GetUserByName, GetUser and ListUsers

### Changes

- Removed the need for keeping authentication information in the integration test config file.  The test runner now looks for a **.openstack_net** file in the users local directory.  
- Fixed a few minor bugs
- Pulled out the Rackspace specific internal admin methods from the __IIdentityProvider__ interface and moved them to a sub interface called __IExtendedIdentityProvider__ since these will not be supported by other openstack instances.
- Fixed the Authentication method to not get the user access token from cache, but instead to ALWAYS make a call to the service.  However, the GetToken methods (used by all other providers to get a token) will use the cache.  
- Added methods to get and update user credencials
- Added missing tests for IdentityProvider methods: Authenticate, ListUsers, GetUserByName and GetUser