BUG: Fix Index.__repr__ when `display.max_seq_items` = 1
- [x] closes #38415 
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Thanks @skvrahul for the PR. please add a test. @jreback @simonjayhawkins 
Could you confirm that this parameter is expected to affect even the list of names of columns in the index
I.e. `repr` evaluates to:
```
MultiIndex([...
            ('qux', 'two')],
           names=['first', ...], length=6)
```
and not
```
MultiIndex([...
            ('qux', 'two')],
           names=['first', 'second'], length=6)
``` > Could you confirm that this parameter is expected to affect even the list of names of columns in the index
> I.e. `repr` evaluates to:
> 
> ```
> MultiIndex([...
>             ('qux', 'two')],
>            names=['first', ...], length=6)
> ```
> 
> and not
> 
> ```
> MultiIndex([...
>             ('qux', 'two')],
>            names=['first', 'second'], length=6)
> ```

Checked on `master` and can confirm this (parameter affects even the list of column names)
Added tests accordingly.
 @jreback Added tests and moved one of the tests to its own TC.  thanks @skvrahul very nice