A new parameter 'use-nat', True by default will specify if we will setup a nat interface.
if 'use-tap' is Truei (false by default), a tap interface will be connected with a new interface in kvm.
if 'use-tap' and 'use-nat' are True, then virtual machine will have two interfaces, one with tap and
one with nat.

with python 2.6 support that can be still required for initial setup of SlapOS.

even though there are install_requires and setup_requires...