He plugin: switch scalability CSIT failing to find links

This switch scalability job is now failing to scale above aprox 200 switches
recently, when it had been achieving 500 switches (the test's max) consistently.

the reason for failure is that a specific switch port is not discovered in the
response from /restconf/operational/network-topology:network-topology

the test flow is to:

start a mininet topo with 100 switches (linear)
fail if OOM is seen
fail if not all 100 switches are seen
fail if all the ports in linear topo are not correct

– increase by 100 and repeat checks.

in one specific failure, the test at 200 switches passed. Then at 300 switches the
failure came, BUT it came when looking for a port on switch 183 (less than 200 which
was fine in the previous iteration)

The full karaf.log is attached, but this stood out to me:
2016-01-26 04:17:48,882 | ERROR | lt-dispatcher-48 | LocalThreePhaseCommitCohort | 139 - org.opendaylight.controller.sal-distributed-datastore - 1.3.0.SNAPSHOT | Failed to prepare transaction member-1-chn-19-txn-1320 on backend
OptimisticLockFailedException

{message=Optimistic lock failed., errorList=[RpcError [message=Optimistic lock failed., severity=ERROR, errorType=APPLICATION, tag=resource-denied, applicationTag=null, info=null, cause=org.opendaylight.yangtools.yang.data.api.schema.tree.ConflictingModificationAppliedException: Node was deleted by other transaction.]]}

the CSIT job:

https://jenkins.opendaylight.org/releng/user/jluhrsen/my-views/view/openflow%20CSIT/job/openflowplugin-csit-1node-periodic-scalability-daily-only-beryllium/plot/Inventory%20Scalability/