BUG: show time values in repr of high precision DatetimeIndex
- [ ] closes #19030 
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

On master:
```
In [2]: pd.DatetimeIndex(['2017-01-01 23:59:59.999999999'])
Out[2]:  DatetimeIndex(['2017-01-01'], dtype='datetime64[ns]', freq=None)
```
On my branch:
```
In [3]: pd.DatetimeIndex(['2017-01-01 23:59:59.999999999'])
Out[3]: DatetimeIndex(['2017-01-01 23:59:59.999999999'], dtype='datetime64[ns]', freq=None)
```
It seems that it's only a problem when the time value was 23:59:59.999999999 or very similar, but I may need to add some more tests to check this further.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19109?src=pr&el=h1) Report
> Merging [#19109](https://codecov.io/gh/pandas-dev/pandas/pull/19109?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/36a71eb00ea61c4e6aef78b9ad9f865760a3cfd4?src=pr&el=desc) will **increase** coverage by `0.02%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/19109/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/19109?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #19109      +/-   ##
==========================================
+ Coverage   91.51%   91.53%   +0.02%     
==========================================
  Files         148      148              
  Lines       48753    48753              
==========================================
+ Hits        44616    44628      +12     
+ Misses       4137     4125      -12
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.91% <ø> (+0.02%)` | :arrow_up: |
| #single | `41.6% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/19109?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/formats/format.py](https://codecov.io/gh/pandas-dev/pandas/pull/19109/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvZm9ybWF0LnB5) | `96.24% <ø> (ø)` | :arrow_up: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/19109/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `66.95% <0%> (+1.73%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19109?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19109?src=pr&el=footer). Last update [36a71eb...aaa1f0c](https://codecov.io/gh/pandas-dev/pandas/pull/19109?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Hello @reidy-p! Thanks for updating the PR.





Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on January 07, 2018 at 12:38 Hours UTC thanks @reidy-p 