C: delete ds benchmark regression

Based on the graph https://jenkins.opendaylight.org/releng/view/controller/job/controller-csit-3node-periodic-benchmark-all-carbon/plot/getPlot?index=6&width=900&height=900 there is regression in DELETE operation.

The comparison is done for builds #130 and #170
https://logs.opendaylight.org/releng/jenkins092/controller-csit-3node-periodic-benchmark-only-carbon/130/archives/
https://logs.opendaylight.org/releng/jenkins092/controller-csit-3node-periodic-benchmark-only-carbon/170/archives/

The log files canbe taken from the links above.
Log files odl1_karaf.log.gz and odl2_karaf.log.gz are huge after unzipping and are full of lines like
2017-02-02 12:54:11,425 | WARN | tp1150926568-510 | SimpletxDomRead | 294 - org.opendaylight.controller.dsbenchmark - 1.3.0.SNAPSHOT | optionalDataObject is either null or .isPresent is false

The regression happened only for config datastore (both leader and follower), operational was not affected.