Upgrade the ew.py script and remove all contrib/conf scripts.
- Give the ew.py script more control over the machine (so far only QEMU),
by allowing the user to choose the NIC, disable networking, hard disk,
USB, sound or KVM.
- ew.py can now do a dry-run, only printing the command line for the
emulator.
- Configuration of machines is now more exception-oriented, meaning that
we attempt to configure the machine with as many features as possible
and allow individual configurations to opt-out e.g. from networking
or sound.