Adds Windows Support to satori discovery

This change adds the capability to satori to do data plane discovery on Windows devices.
For that, a class has been added that mirrors the functionality of satori/ssh.py and
utilizes a "3rd party" script (satori/contrib/psexec.py) which is called via subprocess.Popen().
Further to that, an SSH tunneling class has been put in place that uses paramiko to establish
a tunnel (similar to running ssh -L from a shell). requirements.txt has been extended to
include impacket which satori/contrib/psexec.py imports.

adressing part of Ziad's comments

using improved impacket version

Implements: blueprint windows-support

Change-Id: I7a94eea9446bc7f57843407fb98880222f7af6af
Merge branch 'bp/windows-support' of https://github.com/nick-o/satori into bp/windows-support

Conflicts:
	satori/contrib/psexec.py

Change-Id: I0140e660bdee269bf947bba9c294ebe4d145ddce