produce-transactions does not unregister the producer on error

This happened in CSIT, when the first test [0] failed on CONTROLLER-1678 but the second test failed on IllegalArgumentException [1]:
Caused by:</h3><pre>java.lang.IllegalArgumentException: Subtree DOMDataTreeIdentifier{datastore=CONFIGURATION, root=/(tag:opendaylight.org,2017:controller:yang:lowlevel:target?revision=2017-02-15)id-ints/id-int/id-int[

{(tag:opendaylight.org,2017:controller:yang:lowlevel:target?revision=2017-02-15)id=prefix-2}

]} is attached to producer org.opendaylight.mdsal.dom.broker.ShardedDOMDataTreeProducer@46ff63d8

The previous suite was making sure [2] no producer is running, so this is probably a bug in ODL (as opposed to a bug in the test code).

We can work around this by performing hard resets between tests.

[0] https://logs.opendaylight.org/releng/jenkins092/controller-csit-3node-clustering-only-carbon/684/archives/log.html.gz#s1-s39-t1-k2-k14-k1-k1-k1-k1-k1-k1-k2-k1-k1-k1
[1] https://logs.opendaylight.org/releng/jenkins092/controller-csit-3node-clustering-only-carbon/684/archives/log.html.gz#s1-s39-t2-k2-k14-k1-k1-k1-k1-k1-k1-k1-k1-k1-k1
[2] https://logs.opendaylight.org/releng/jenkins092/controller-csit-3node-clustering-only-carbon/684/archives/log.html.gz#s1-s39-t1-k2-k15-k3