keep_tz FutureWarning and generic.py
#### Code Sample, a copy-pastable example if possible

```python
import pandas as pd
df = pd.DataFrame(index=pd.date_range(start='2019', periods=3, freq='H', tz='America/Los_Angeles'), data={'A': [1, 2, 3]})
df.query('A > 1')
```
#### Problem description

The above code produces a `FutureWarning`:

```
/usr/local/lib/python3.6/dist-packages/pandas/core/generic.py:407: FutureWarning: The default of the 'keep_tz' keyword will change to True in a future release. You can set 'keep_tz=True' to obtain the future behaviour and silence this warning.
  s = level_values.to_series()
/usr/local/lib/python3.6/dist-packages/pandas/core/generic.py:415: FutureWarning: The default of the 'keep_tz' keyword will change to True in a future release. You can set 'keep_tz=True' to obtain the future behaviour and silence this warning.
  dindex = axis_index.to_series()
```

#### Expected Output

I believe the internal pandas code (`generic.py`) needs to handle the warning by passing an appropriate keyword (`keep_tz=True`).

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

<details>

commit: None
python: 3.6.8.final.0
python-bits: 64
OS: Linux
OS-release: 4.15.0-52-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_CA.UTF-8
LOCALE: en_CA.UTF-8

pandas: 0.24.2
pytest: 4.0.0
pip: 19.1.1
setuptools: 40.4.3
Cython: 0.29.10
numpy: 1.16.4
scipy: 1.3.0
pyarrow: None
xarray: None
IPython: 7.5.0
sphinx: None
patsy: 0.5.0
dateutil: 2.7.3
pytz: 2018.3
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: 3.1.0
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml.etree: 4.2.1
bs4: None
html5lib: 1.0.1
sqlalchemy: 1.3.1
pymysql: None
psycopg2: 2.8.2 (dt dec pq3 ext lo64)
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: 0.9.0
pandas_datareader: None
gcsfs: None



</details>
