Drop neutron masking exception in vif_attach
Drop neutron masking exception in vif_attach

This patch drops masking exceptions when try to get physnets for
ports in vif_attach as neutron is mandatory when using flat, neutron
network interfaces.
Api tests were reworked 5cb1720b6e1f2f799a3282828c317f1ef29b2189 to use
real neutron port.

Change-Id: Ic1138e6da790bfe6903d13b548c230187b119a3d

openstack/ironic,openstack/ironic