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>
Hey, @FengYang, I found there was no timeout for self.login to get VM's address in ff5a257..84e6e20 .
But in the scene that vm‘s booting time is long enough or vm is running(no tcpdump info for vm),
we will miss the get_address if serial is not configured in this one time addressing.

So, I think a timeout for getting address is essential, what's your idea?
Maybe we can think about renovating wait_for_get_address to save 
waited time instead of do once checking.