instance/network: allow to select compute interface, previously only compute network

instances/templates/add_instance_network_block.html

@@ -25,7 +25,10 @@
                             <div class="col-sm-6">
                                 <select class="form-control" name="add-net-network">
                                     {% for c_net in compute_networks %}
-                                        <option value="{{ c_net }}">{{ c_net }}</option>
+                                        <option value="net:{{ c_net }}">Network {{ c_net }}</option>
+                                    {% endfor %}
+                                    {% for c_iface in compute_interfaces %}
+                                        <option value="iface:{{ c_iface }}">Interface {{ c_iface }}</option>
                                     {% endfor %}
                                 </select>
                             </div>