Add support for connecting to VMs through a serial port

[c4milo]

This is not critical at all, just fun to do.

It will be nice to be able to log into the virtual machines through a serial communication in case SSH dies (which is very unlikely but happens once in a while)

http://thewayeye.net/2009/december/4/connecting-virtual-machines-serial-console-os-x-and-vmware-fusion

[c4milo]

All is in the place in https://github.com/cloudescape/govmx for this to be easily implemented.