[Clients] Add classmethod osclients.Clients.register

Classmethod osclients.Clients.register allows to add new
OpenStack clients to Rally at runtime, so these clients will
be available from osclients.Clients and cached.

Change-Id: I644aa2b742a8433f90068ae95328f5d0ef6b27dc

rally/osclients.py

@@ -429,3 +429,29 @@ class Clients(object):
             if service_type in consts.ServiceType:
                 services_data[service_type] = consts.ServiceType[service_type]
         return services_data
+
+    @classmethod
+    def register(cls, client_name, client_func):
+        """Add new OpenStack client dynamically.
+
+        :param client_name: str name how client will be named in Rally clients
+        :param client_func: function that implememnts client spawning.
+                            It will be added to Clients in runtime, so its
+                            sole argument is Clients instance
+        Example:
+          >>> def supernova(self):
+          ...   from novaclient import client as nova
+          ...   return nova.Client("2", auth_token=self.keystone().auth_token,
+          ...                      **self._get_auth_info(password_key="key"))
+          ...
+          >>> from rally import osclients
+          >>> osclients.Clients.register("supernova", supernova)
+          >>> clients = osclients.Clients.create_from_env()
+          >>> clients.supernova().services.list()[:2]
+          [<Service: nova-conductor>, <Service: nova-cert>]
+        """
+        if hasattr(cls, client_name):
+            raise ValueError(
+                _("Can not register client: name already exists: %s")
+                % client_name)
+        setattr(cls, client_name, cached(client_func))

tests/unit/test_osclients.py

@@ -465,3 +465,22 @@ class OSClientsTestCase(test.TestCase):
                   "token": self.fake_keystone.auth_token}
             mock_murano.client.Client.assert_called_once_with("1", **kw)
             self.assertEqual(fake_murano, self.clients.cache["murano"])
+
+    @mock.patch("rally.osclients.cached")
+    def test_register(self, mock_cached):
+        client_func = mock.Mock(return_value="foo_client")
+        cached_client_func = mock.Mock(return_value="cached_foo_client")
+        mock_cached.return_value = cached_client_func
+        clients = osclients.Clients(mock.Mock())
+
+        self.assertFalse(hasattr(clients, "foo"))
+
+        osclients.Clients.register("foo", client_func)
+
+        mock_cached.assert_called_once_with(client_func)
+        self.assertEqual("cached_foo_client", clients.foo())
+        self.assertEqual(cached_client_func, clients.foo)
+
+        # Call second time with same name
+        self.assertRaises(ValueError,
+                          osclients.Clients.register, "foo", client_func)