PR to upstream features and fixes from Cisco fork

[dani-maarouf]

Hello!

We have an internal fork of this repo which we are using at Cisco. This PR is to upstream the changes which were added in that fork.

This changeset adds the following features:

• support multiple serial ports for one VM
• support for exclusive (at most 1 client) access to a VMs console
• support for 'line clearing' (kick off any clients connected to a VMs console), like a terminal server

There were also some logging enhancements, particularly in telnetlib.py

There are some bug fixes as well, including e.g. fixing some unicode conversion issues