Rename ServiceClient to ProviderClient.

Rather than store state within service-level Clients, we really want that
at the provider level. Service-level clients should be stateless.
diff --git a/openstack/identity/v3/tokens/urls_test.go b/openstack/identity/v3/tokens/urls_test.go
index 5ff8bc6..5007b3d 100644
--- a/openstack/identity/v3/tokens/urls_test.go
+++ b/openstack/identity/v3/tokens/urls_test.go
@@ -11,7 +11,7 @@
 	testhelper.SetupHTTP()
 	defer testhelper.TeardownHTTP()
 
-	client := gophercloud.ServiceClient{Endpoint: testhelper.Endpoint()}
+	client := gophercloud.ProviderClient{Endpoint: testhelper.Endpoint()}
 
 	expected := testhelper.Endpoint() + "auth/tokens"
 	actual := getTokenURL(&client)