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

[alanquillin]

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