Provisioned subscriber is not cleared at ONOS sometime after OLT delete

https://jenkins.opencord.org/view/VOLTHA-2.X-Tests/job/build_flex-ocp-cord_Default_voltha_master_test/570/robot/report/FailureScenarios/log.html

• Sanity E2E Test for OLT/ONU on POD With Core Fail and Restart

Failed because DHCP did not succeed for subscriber on port 4112.

Root cause:
The test starts with OLT delete. After OLT delete, the subscriber on port 4112 did not get cleared from ONOS.
Later when subscriber was provisioned again, ONOS ignores the request saying the subscriber is already provisioned.
This means that flow is not installed on the OLT/ONU and DHCP packet is not processed.

Also happens in 

https://jenkins.opencord.org/view/VOLTHA-2.X-Tests/job/build_onf-demo-pod_1T8GEM_voltha_DT_master_test/332/robot/report/dt-workflow/FailureScenarios/log.html

• Verify OLT after Rebooting Physically for DT
  Failed because ONU is not in right state - expected omci-flows-pushed but it is in initial-mib-downloaded state. Same as VOL-3776

Root cause:
The previous test deletes the OLT the end of the test, but for some reason one of the provisioned subscriber is not cleared.
In the current test, when the subscriber is provisioned again, the flows are not pushed to voltha (because the subscriber already exists in voltha)
and hence the ONU is stuck in initial-mib-downloaded state.

Attached logs from both the tests here.