Enable osc extension in setup.cfg
Enable osc extension in setup.cfg

This patch removes changes from previous patch
Iaf74c264fb9d92a9fce9d5d19c48b54b88a40ad7 .
Now osc extension is enabled and can be used for continue development
support of openstackclient.

Change-Id: Iccff66327bc29075d85801d8b6fa418963fa5c88

openstack/python-heatclient