This patch will add the support for parameter skip_host_detach in
LogicalPort deletion request as the preparation of a corner fix
which will delete the discovered port without host detach.
The other preparation in this patch is to add the new Exception
class VifRestoreAlreadyCompleted.
Change-Id: I012dbc7db5c0af31d670e71e1d04fa6216f269b3
d11fe387c7