ovn: Override clean_hash_ring for sync util
ovn: Override clean_hash_ring for sync util

ML2 OVN Mechanism driver wipes all the nodes from ovn_hash_ring table on
initialization. The DB sync untility inherits from the mechanism driver
calling the cleanup whenever sync util is executed. This leads to nodes
being deleted while neutron-server is typically running, causing serious
issues to neutron-server until it is restarted.

This patch overrides the clean method to no-op.

Change-Id: I5ea8278c0387009ff429572662d64e7664f493e7
Closes-Bug: #1879950
Signed-off-by: Jakub Libosvar <d2de8475ecde4f30221bae835ec23b041ec4f992@redhat.com>

mahak/neutron,openstack/neutron,mahak/neutron,openstack/neutron,openstack/neutron,mahak/neutron