allow to config port binding:profile

When using OVS HW offload feature we need to create
neutron port with  --binding-profile '{"capabilities": ["switchdev"]}' [1]
To allow this feature to be tested with Mellanox CI we need a way
to configure the port binding:profile in tempest

[1] - https://review.openstack.org/#/c/504911/

Change-Id: I9b562aaabf960d38f623d88e8b88619edbb70fe8
diff --git a/tempest/config.py b/tempest/config.py
index 340a27e..8a6370a 100644
--- a/tempest/config.py
+++ b/tempest/config.py
@@ -609,10 +609,14 @@
                      " for subnet creation"),
     cfg.StrOpt('port_vnic_type',
                choices=[None, 'normal', 'direct', 'macvtap'],
-               help="vnic_type to use when Launching instances"
+               help="vnic_type to use when launching instances"
                     " with pre-configured ports."
                     " Supported ports are:"
                     " ['normal','direct','macvtap']"),
+    cfg.DictOpt('port_profile',
+                default={},
+                help="port profile to use when launching instances"
+                     " with pre-configured ports."),
     cfg.ListOpt('default_network',
                 default=["1.0.0.0/16", "2.0.0.0/16"],
                 help="List of ip pools"