BUG: to_datetime drops UTC offset when parsing datetime strings and box=False
xref https://github.com/pandas-dev/pandas/pull/22380#issuecomment-413617891 and post PR #21822

```
In [1]: data = ['2018-01-04 09:01:00+09:00', '2018-01-04 09:02:00+09:00']

# This output should behave like Out[5]
In [3]: pd.to_datetime(data, box=False)
Out[3]:
array(['2018-01-04T00:01:00.000000000', '2018-01-04T00:02:00.000000000'],
      dtype='datetime64[ns]')

In [4]: data = ['2018-01-04 09:01:00+09:00', '2018-01-04 09:02:00+08:00']

In [5]: pd.to_datetime(data, box=False)
Out[5]:
array([datetime.datetime(2018, 1, 4, 9, 1, tzinfo=tzoffset(None, 32400)),
       datetime.datetime(2018, 1, 4, 9, 2, tzinfo=tzoffset(None, 28800))],
      dtype=object)
```