[libvirt] Enhancement: Random Clock Offset

[bancfc at openmailbox.org]

For better system anonymity (to decouple VM OS timestamps leaked in 
traffic from host ones) a feature can be added to the clock offset 
variable to select randomly from a specified range of seconds from 
instead of a fixed  number of seconds. That way a guest's clock can vary 
unpredictably from the host's and confuse  correlation by network 
adversaries.

Full Disclosure: I am from the  Tor centric Whonix Project - whonix.org 
and this would be a very useful feature for us.