network elements (nodes, links, etc) are not always removed when running longevity test

two jobs that sometimes fail:
https://jenkins.opendaylight.org/releng/view/openflowplugin/job/openflowplugin-csit-1node-periodic-longevity-lithium-redesign-only-beryllium/

https://jenkins.opendaylight.org/releng/view/openflowplugin/job/openflowplugin-csit-1node-periodic-longevity-only-beryllium/

The basic flow of the job is to bring up 200 switches (mininet, linear topo) and
verify that they are connected and proper links via operational store. Then the
network is stopped and it's verified to be removed.

When the test fails, it seems to always be because the network has been stopped,
but there are still some things showing up in the call to /restconf/operational/network-topology:network-topology

It seems that it takes many iterations (e.g. 50-ish iterations taking 6-10 hours) to
hit this problem. No further root cause analysis has been done at this time.