MultiIndex with dates gives wrong output for values()
Calling `values()` on a `MultiIndex` with date_ranges returns an array of tuples of Timestamp, instead of an array of Timestamp. I think this is a bug... is this expected?

```python
>>> idx = pd.MultiIndex(levels=[pd.date_range("20170103", "20170105", tz='UTC')], labels=[[0, 1, 2]])                                                                                                                                                                                                                         
>>> idx.values                                                                                                                                                                                                                                                                                                                
array([(Timestamp('2017-01-03 00:00:00+0000', tz='UTC', freq='D'),),                                                                                                                                                                                                                                                          
       (Timestamp('2017-01-04 00:00:00+0000', tz='UTC', freq='D'),),                                                                                                                                                                                                                                                          
       (Timestamp('2017-01-05 00:00:00+0000', tz='UTC', freq='D'),)],                                                                                                                                                                                                                                                         
      dtype=object) 

```
#### Problem description

As shown above, `values()` returns an array with tuples, instead of the expected array of Timestamp.


#### Versions

<details>

pandas==0.22
numpy==1.14.2
python==2.7.13

</details>
