Init placement client in tempest Manager object

Placement client is not yet added/initialized in
the tempest/clients.py Manager object.

Change-Id: I19224b178e2860ee29c56546340cee36cd71b0e8
diff --git a/tempest/clients.py b/tempest/clients.py
index e5d5be1..0506646 100644
--- a/tempest/clients.py
+++ b/tempest/clients.py
@@ -44,6 +44,7 @@
         self._set_object_storage_clients()
         self._set_image_clients()
         self._set_network_clients()
+        self.placement_client = self.placement.PlacementClient()
         # TODO(andreaf) This is maintained for backward compatibility
         # with plugins, but it should removed eventually, since it was
         # never a stable interface and it's not useful anyways