Network ignore list

In certain cloud node, it has multiple network interfaces which makes hard to run network performance test because it uses all network interfaces available to make TinCan connection. It is necessary to configure which network interfaces are not to be used. 
We can specify the network interfaces to be ignored in the config file as below. 
```
"network_ignore_list": ["virbr0", "wlan0", "lxcbr0"]
```
Colleagues from VU demanded this feature.