'Create sample rings with four devices
:returns: a list of ring builder instances'

def create_sample_ringbuilders(self, num_builders=2, rebalance=True):

    builders = []
    for region in range(num_builders):
        fname = os.path.join(self.tmpdir, ('builder_%s.builder' % region))
        builder = RingBuilder(6, 3, 0)
        for _ in range(5):
            dev = self.pop_region_device(region)
            builder.add_dev(dev)
        builder.remove_dev(dev['id'])
        new_dev = self.pop_region_device(region)
        new_dev['weight'] = 0
        builder.add_dev(new_dev)
        if rebalance:
            builder.rebalance()
        builder.save(fname)
        self.assertTrue(os.path.exists(fname))
        builders.append(builder)
    return builders
