Exception when calling read_gbq : No module named discovery
I ran into the following exception when using the pandas `read_gbq()` function.

```
      1 import pandas as pd
----> 2 pd.read_gbq('select * from SampleDataset.SampleTable', project_id='xxxxxxx')

/usr/local/lib/python2.7/dist-packages/pandas/io/gbq.pyc in read_gbq(query, project_id, index_col, col_order, reauth, verbose)
    425         job_id = uuid.uuid4().hex
    426         rows = []
--> 427         remaining_rows = len(dataframe)
    428 
    429         if self.verbose:

/usr/local/lib/python2.7/dist-packages/pandas/io/gbq.pyc in __init__(self, project_id, reauth)
    111     not match the schema of the destination
    112     table in BigQuery.
--> 113     """
    114     pass
    115 

/usr/local/lib/python2.7/dist-packages/pandas/io/gbq.pyc in test_google_api_imports(self)
    127     Raised when BigQuery reports a streaming insert error.
    128     For more information see `Streaming Data Into BigQuery
--> 129     <https://cloud.google.com/bigquery/streaming-data-into-bigquery>`__
    130     """
    131 

ImportError: Missing module required for Google BigQuery support: No module named discovery
```

An exception occurs in `test_google_api_imports()` . I believe the issue is on line 49 in https://github.com/pydata/pandas/blob/master/pandas/io/gbq.py . 

We use

```
from apiclient.discovery import build
```

instead of

```
from googleapiclient.discovery import build
```

`apiclient` is an alias for `googleapiclient` according to https://github.com/google/google-api-python-client/blob/master/apiclient/__init__.py#L1

A similar issue is reported here: https://github.com/google/google-api-python-client/issues/13

`apiclient.__version__` fails

```
>> import apiclient
>> apiclient.__version__
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-90-662a0f56e34b> in <module>()
      1 import apiclient
----> 2 apiclient.__version__

AttributeError: 'module' object has no attribute '__version__'
```

`googleapiclient.__version__` works

```
import googleapiclient
googleapiclient.__version__
```

```

INSTALLED VERSIONS
------------------
commit: None
python: 2.7.9.final.0
python-bits: 64
OS: Linux
OS-release: 3.16.0-4-amd64
machine: x86_64
processor: 
byteorder: little
LC_ALL: None
LANG: None

pandas: None
nose: 1.3.7
pip: 1.5.6
setuptools: 5.5.1
Cython: 0.24
numpy: 1.10.4
scipy: 0.17.0
statsmodels: 0.6.1
IPython: 4.0.3
sphinx: None
patsy: 0.4.1
dateutil: 2.4.2
pytz: 2015.7
blosc: None
bottleneck: None
tables: None
numexpr: None
matplotlib: 1.5.1
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: 0.999
httplib2: 0.9.2
apiclient: 1.5.1
sqlalchemy: None
pymysql: None
psycopg2: None
Jinja2: None
```
