A script to invoke qemu properly under a variety of settings.

A script to invoke qemu properly under a variety of settings.

Supports:
- VDE for networking of multiple qemu instances (e.g., plc head + node).
- USER networking as provided by qemu.
- Can redirect console output to terminal.  No need for graphics or
  X-windows.  Hopefully this will ease automated testing.

Not fully tested:
- multihoming support
- loading vm snapshots
- SMP

Not at all supported:
- TAP networking