Metadata port creation would fail if the openvswitch is in crashed state and neutron-opflex-agent is being restarted

[deshshukla]

Based on the code https://github.com/noironetworks/python-opflex-agent/blob/master/opflexagent/as_metadata_manager.py#L693-L722, the metdata port wiring happens only during the initialization of the service, if the openvswitch service is not functional at the agent startup, the metadata port creation fails silently

An exception should be raised and neutron-opflex-agent should report a startup failure stating the dependent service (openvswitch) is unhealthy.