Fix URLs to use v3 when only v2 endpoint is listed in the catalog

It covers the cases where we can authenticate with keystone v3 but the endpoint returned in the catalog is v2
see #492

lib/fog/openstack/core.rb

@@ -222,6 +222,11 @@ def authenticate
                                         @openstack_auth_url
                                       end
 
+          # Manages cases where identity endpoint returned is v2 but v3 should be used
+          if @openstack_service_type.include? 'identity_v3' and @openstack_management_url =~ /\/v2.0(\/)*$/
+            @openstack_management_url = @openstack_auth_url
+          end
+
           @current_user = token.user['name']
           @current_user_id          = token.user['id']
           @current_tenant           = token.tenant