Bug:995-Controller does not learn node connectors from mininet OF10

- replaced shutdownNow with shutdown+purge

Change-Id: Ia9f299fd5e46d13a9bbd9d28925ca4e758ec46ec
Signed-off-by: Kamal Rameshan <kramesha@cisco.com>
Signed-off-by: Michal Rehak <mirehak@cisco.com>