Add NMap tool for getting IP.

In some condition, vm may have fixed IP, but tcpdump couldn't get it until some packaged sent.
So can we start another tool 'nmap' parallel when tcpdump is working?
Following codes are simple description of this tool, just for hints. :)  

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
No, reset them to None to start another round for ip and mac.
Because the result looks like:
```
Nmap scan report for 10.167.226.115
Host is up (0.0015s latency).
Not shown: 998 filtered ports
PORT     STATE SERVICE
135/tcp  open  msrpc
3389/tcp open  ms-wbt-server
MAC Address: 00:1D:0F:1F:67:2B (Tp-link Technologies Co.)

Nmap scan report for 10.167.226.117
Host is up (0.0011s latency).
Not shown: 995 filtered ports
PORT     STATE SERVICE
23/tcp   open  telnet
135/tcp  open  msrpc
139/tcp  open  netbios-ssn
445/tcp  open  microsoft-ds
3389/tcp open  ms-wbt-server
MAC Address: 44:37:E6:18:83:4C (Hon Hai Precision Ind.Co.Ltd)
```
The end of MAC means we got them both.