Adding the ability to use pre-created ports in Network scenarios

It's possible to launch an instance with virtual interfaces
either by specifying the network the interface should be attached
to or the port.
There are cases (e.g. SR-IOV) where it's only possible to launch
an instance with a pre-created port.
Enabling the creation of  a port with known vnic_types (Currently
'normal','direct' and 'macvtap') and launching an instance with this port
attached.

Nova support Neutron SR-IOV ports https://wiki.openstack.org/wiki/Nova-neutron-sriov

Change-Id: Id5cbd50d285ac0c7e8099c30151ace9d99f02020
diff --git a/etc/tempest.conf.sample b/etc/tempest.conf.sample
index 0eeb738..bc4198f 100644
--- a/etc/tempest.conf.sample
+++ b/etc/tempest.conf.sample
@@ -779,6 +779,10 @@
 # value)
 #dns_servers = 8.8.8.8,8.8.4.4
 
+# vnic_type to use when Launching instances with pre-configured ports.
+# Supported ports are: ['normal','direct','macvtap'] (string value)
+#port_vnic_type = <None>
+
 
 [network-feature-enabled]