'cpu: desired overall system CPU fraction
cores: (real) core(s) this host can run on
params: parameters for Node.config()'

def config(self, cpu=(-1), cores=None, **params):

    r = Node.config(self, **params)
    self.setParam(r, 'setCPUFrac', cpu=cpu)
    self.setParam(r, 'setCPUs', cores=cores)
    return r
