BUG: repr on DTI with high precision is wrong
SO the value is correct
```
In [2]: pd.DatetimeIndex(['2017-01-01 23:59:59.999999999'])
Out[2]: DatetimeIndex(['2017-01-01'], dtype='datetime64[ns]', freq=None)

In [3]: pd.DatetimeIndex(['2017-01-01 23:59:59.999999999']).values
Out[3]: array(['2017-01-01T23:59:59.999999999'], dtype='datetime64[ns]')
```

and lower precision is ok
```
In [4]: pd.DatetimeIndex(['2017-01-01 23:59:59.999999'])
Out[4]: DatetimeIndex(['2017-01-01 23:59:59.999999'], dtype='datetime64[ns]', freq=None)
```

but the ns is causing issues.