TST/BUG: DataFrame truncated repr with DatetimeTz and NaT column
- [x] closes #12211
- [x] tests added / passed
- [x] passes `git diff upstream/master | flake8 --diff`

## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/13039?src=pr) is **84.06%**

> Merging [#13039](https://codecov.io/gh/pydata/pandas/pull/13039?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will decrease coverage by **-0.00%**

``` diff
@@             master     #13039   diff @@
==========================================
  Files           136        136          
  Lines         49994      49994          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
- Hits          42028      42027     -1   
- Misses         7966       7967     +1   
  Partials          0          0          
```
1. File `...das/tseries/index.py` (not in diff) was modified. [more](https://codecov.io/gh/pydata/pandas/commit/44d2e2b132b837cdd5f2062aadb55ccaef6689c4/changes?src=pr#70616E6461732F747365726965732F696E6465782E7079) 
   - Misses `+1` 
   - Partials `0` 
   - Hits `-1`

> Powered by [Codecov](https://codecov.io?src=pr). Last updated by [84725fa...44d2e2b](https://codecov.io/gh/pydata/pandas/compare/84725fa936b4136657f5ea02c588790de6866899...44d2e2b132b837cdd5f2062aadb55ccaef6689c4)
