to fix IllegalStateException due to DOMBrokerTransactionChain !equals
TracingTransactionChain (only affected odl-mdsal-trace for
trace:transaction anyway)
see https://jira.opendaylight.org/browse/CONTROLLER-1792
Change-Id: I079ff9e99edfd55bec2acbe1984a5c2b7667c2de Signed-off-by: Michael Vorburger <vorburger@redhat.com>