become-prefix-leader does not work if there is producer active on the target member

Robot sees [0] this and reports:
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@2cd65513

Looking at the current implementation, PrefixLeaderHandler is using a temporary CDSDataTreeProducer, which would be targeted to an ancestor prefix of the active producer prefix.

One possible fix would be to give PrefixLeaderHandler access to ProduceTransactionsHandler (if it exists) created by produce-transactions on the same member, to use its producer (to get the shard access) instead of the temporary one.

[0] https://logs.opendaylight.org/releng/jenkins092/controller-csit-3node-clustering-only-carbon/697/archives/log.html.gz#s1-s26-t5-k2-k6-k3-k1-k4-k7-k1