BUG: preserve DatetimeIndex.name in HDFStore/read_hdf() with tz (#13884)
- [x] closes #13884
- [x] tests added / passed
- [x] passes `git diff upstream/master | flake8 --diff`
- [x] whatsnew entry

tests!
 @jreback I added a test now (still just one commit).
 lgtm. pls add a whatsnew note in Bug Fixes.
 ping on green.
 ## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/13888?src=pr) is 85.29% (diff: 100%)

> Merging [#13888](https://codecov.io/gh/pydata/pandas/pull/13888?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will decrease coverage by **<.01%**

``` diff
@@             master     #13888   diff @@
==========================================
  Files           139        139          
  Lines         50087      50088     +1   
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
  Hits          42723      42723          
- Misses         7364       7365     +1   
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last update [0be0d67...789fa59](https://codecov.io/gh/pydata/pandas/compare/0be0d679873234bfa5198e27a213afe8d43edad7...789fa5926e0a7be58746563458f6d94e06537e69?src=pr)
 @jreback ping, this is good to go.
 thanks!
