Test port data plane status on Sample Inspector

Test port data plane status on Sample Inspector

Exercise the Neutron port data plane status API on the Sample Inspector.

Setting the data_plane_status field of Neutron Port objects to 'DOWN'
when a network failure on a node is detected.

To keep the test simple enough to verify the Neutron API, we don't
consider a scenario where multiple NIC ports could be present on that
particular node. It could still be done, though.

JIRA: DOCTOR-107

Change-Id: I9ffa0a23626b7edfaeb601dc90d55c756216cc41
Signed-off-by: Carlos Goncalves <carlos.goncalves@neclab.eu>