Update vif_attach from NeutronVIFPortIDMixin

This patch updates vif_attach from NeutronVIFPortIDMixin to rely
on presence of Neutron. Drop incorrect logic that skips mac_address
update when show_port() to neutron failed as NeutronVIFPortIDMixin
is used only in flat and neutron network interfaces which require
neutron presence.
Update api tests to use real neutron port.

Change-Id: Iffaf3569aa296b4466729cf7f62c92995b6b3723
1 file changed