Different results with tzlib and dateutil_tz with "ambiguous" argument to tz_localize 
#### Code Sample, a copy-pastable example if possible

```python
In [2]: import pytz

In [3]: pytz_tz = pytz.timezone('US/Eastern')
   ...: dateutil_tz = pd._libs.tslib.maybe_get_tz('dateutil/US/Eastern')
   ...: 

In [4]: idx = pd.DatetimeIndex(['2011-11-06 01:00:00'])

In [5]: l1 = idx.tz_localize(pytz_tz, ambiguous=[1])

In [6]: l2 = idx.tz_localize(dateutil_tz, ambiguous=[1])

In [7]: l1 == l2
Out[7]: array([ True], dtype=bool)

In [8]: l1[0] == l2[0]
Out[8]: True

In [9]: str(l1[0]) == str(l2[0])
Out[9]: False

In [10]: l1, l2
Out[10]: 
(DatetimeIndex(['2011-11-06 01:00:00-04:00'], dtype='datetime64[ns, US/Eastern]', freq=None),
 DatetimeIndex(['2011-11-06 01:00:00-05:00'], dtype='datetime64[ns, tzfile('/usr/share/zoneinfo/US/Eastern')]', freq=None))
```
#### Problem description

I guess (and the existing tests suggest) the two should produce the same results.

#### Expected Output

``l1`` and ``l2`` should be perfectly equivalent I guess.

#### Output of ``pd.show_versions()``

<details>
INSTALLED VERSIONS
------------------
commit: 1002cc339d81591b280ec3ec3c8ac58ce157e3b6
python: 3.5.3.final.0
python-bits: 64
OS: Linux
OS-release: 4.7.0-1-amd64
machine: x86_64
processor: 
byteorder: little
LC_ALL: None
LANG: it_IT.utf8
LOCALE: it_IT.UTF-8

pandas: 0.20.0rc1+53.g1002cc339
pytest: 3.0.6
pip: 9.0.1
setuptools: 33.1.1
Cython: 0.25.2
numpy: 1.12.1
scipy: 0.18.1
xarray: 0.9.1
IPython: 5.1.0.dev
sphinx: 1.4.9
patsy: 0.3.0-dev
dateutil: 2.5.3
pytz: 2016.7
blosc: None
bottleneck: 1.2.0
tables: 3.3.0
numexpr: 2.6.1
feather: 0.3.1
matplotlib: 2.0.0
openpyxl: 2.3.0
xlrd: 1.0.0
xlwt: 1.1.2
xlsxwriter: 0.9.6
lxml: 3.7.1
bs4: 4.5.3
html5lib: 0.999999999
sqlalchemy: 1.0.15
pymysql: None
psycopg2: None
jinja2: 2.8
s3fs: None
pandas_gbq: None
pandas_datareader: 0.2.1


</details>
