Add oslo concurrency namespace

As magnum used concurrency, this patch adds those two options to
generated magnum.conf

see: https://github.com/openstack/oslo.concurrency/blob/master/oslo_concurrency/lockutils.py#L40

Change-Id: I50ece3aed506b27c0c87069cab7aa99c376fc663

tox.ini

@@ -28,6 +28,7 @@ commands = python setup.py build_sphinx
 commands =
     oslo-config-generator --output-file etc/magnum/magnum.conf.sample \
     --namespace magnum \
+    --namespace oslo.concurrency \
     --namespace oslo.db \
     --namespace oslo.messaging \
     --namespace keystonemiddleware.auth_token