Setup and tear down actions. 

Need to implement the following:
@qdev-dk/qcodes   should  there  be the  .run()  in the following snippet ? 

``` python
qc.Measure(vna.s11, vna.s21).setup(..).teardown(..).run(..) 
```

See #263  for more info qc.Measure (not yet implemented). 

``` python
  Loop(..).setup(..).teardown(..).run(..)

```
