Under certain circumstances, net.Interfaces() will begin
returning interfaces in unusual orders (e.g. if the interface
index goes above 255 or 256). This could cause the driver to
select the wrong interface, which in turn would mean that
it could not find a matching VM in vSphere and would crash.
This changeset adds an argument to control what interfaces can
be selected by the driver, by allowing certain interfaces to be
excluded from consideration.