Pandas to_datetime unexpected UTC return
#### Code Sample, a copy-pastable example if possible
```
import pandas
import datetime,time

datetime1 = '2017-03-30T12-00-00'
d = datetime.datetime.strptime(datetime1, "%Y-%m-%dT%H-%M-%S")
s = time.mktime(d.timetuple())

print pandas.to_datetime(datetime1, format = "%Y-%m-%dT%H-%M-%S")
print pandas.to_datetime(s, unit='s')
```
#### Problem description

The outcome datetime is in UTC when converting seconds, although utc option of pandas.to_datetime is defaultly set at None.

#### Expected Output
I expect to have an output in local time when utc option left as deflaut value. Also the utc option as True/False should change the to_datetime method output when it does not.

#### Output of ``pd.show_versions()``
<details>
INSTALLED VERSIONS
------------------
commit: None
python: 2.7.11.final.0
python-bits: 64
OS: Linux
OS-release: 3.10.0-514.10.2.el7.x86_64
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: fr_FR.UTF-8

pandas: 0.17.1
nose: 1.3.7
pip: 9.0.1
setuptools: 30.3.0
Cython: 0.22.1
numpy: 1.10.1
scipy: 0.15.1
statsmodels: None
IPython: 5.1.0
sphinx: 1.3.4
patsy: None
dateutil: 2.4.2
pytz: 2015.7
blosc: None
bottleneck: None
tables: None
numexpr: 2.4.6
matplotlib: 1.4.3
openpyxl: 2.3.4
xlrd: 0.9.4
xlwt: 1.0.0
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: 0.8.2
pymysql: None
psycopg2: 2.6.1 (dt dec pq3 ext)
Jinja2: None
</details>
