Ports created without binding to a host cannot be attached to a VM

If a port is created using "port-create" without specifying host binding, that port cannot be used to boot a VM using "nova boot --nic port-id=<port>".

When a port is created, it may not have a device id or host as the port is not connected to any resource. Since it is not present on any host, the hostbinding is also empty. So when "neutron port-create" results in create_port_*() calls, the Arista ML2 driver does not store the port in the DB and does not send it to EOS.

When the port is used to boot a VM, it results in update_port_*() calls where the device id and the host binding are set. In the update_port_precommit() the driver checks whether the port exists before updating it. Since it was not stored in the DB during the create_port_precommit(), the port is not found in the DB and so it is not updated. in the update_port_postcommit(), the driver again looks into the DB to check whether the port exists. Since it is not found, the port details are not sent to EOS and so the network required for the VM is not provisioned on the switch interface.