Add support for static IPv4 configuration

Signed-off-by: Martin Lucina <martin@lucina.net>
xr: Add -N and -M options

Signed-off-by: Martin Lucina <martin@lucina.net>
xr: Rename to rumprun-xen

Rename the "xr" driver script to "rumprun-xen" to better reflect it's
purpose and scope.

Signed-off-by: Martin Lucina <martin@lucina.net>