Rolling(axis='columns').count() ignores axis= keyword
addtl example on #13753 
#### Code Sample, a copy-pastable example if possible

``` python
In [1]: import pandas as pd

In [2]: df = pd.DataFrame({'x': range(5), 'y': range(5)})

In [3]: df
Out[3]: 
   x  y
0  0  0
1  1  1
2  2  2
3  3  3
4  4  4

In [4]: df.rolling(2, axis='columns').sum()  # meets expectations
Out[4]: 
    x    y
0 NaN  0.0
1 NaN  2.0
2 NaN  4.0
3 NaN  6.0
4 NaN  8.0

In [5]: df.rolling(2, axis='columns').count()  # appears to be the same as axis='rows'
Out[5]: 
     x    y
0  1.0  1.0
1  2.0  2.0
2  2.0  2.0
3  2.0  2.0
4  2.0  2.0

In [6]: df.rolling(2, axis='rows').count()  # yeah, exactly the same
Out[6]: 
     x    y
0  1.0  1.0
1  2.0  2.0
2  2.0  2.0
3  2.0  2.0
4  2.0  2.0
```
#### output of `pd.show_versions()`

``` python
In [7]: pd.show_versions()

INSTALLED VERSIONS
------------------
commit: None
python: 3.5.1.final.0
python-bits: 64
OS: Linux
OS-release: 4.4.0-24-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8

pandas: 0.18.1
nose: 1.3.7
pip: 8.1.1
setuptools: 20.3
Cython: 0.23.4
numpy: 1.10.4
scipy: 0.17.0
statsmodels: 0.6.1
xarray: None
IPython: 4.1.2
sphinx: 1.3.5
patsy: 0.4.0
dateutil: 2.5.1
pytz: 2016.2
blosc: None
bottleneck: 1.0.0
tables: 3.2.2
numexpr: 2.5
matplotlib: 1.5.1
openpyxl: 2.3.2
xlrd: 0.9.4
xlwt: 1.0.0
xlsxwriter: 0.8.4
lxml: 3.6.0
bs4: 4.4.1
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: 1.0.12
pymysql: None
psycopg2: None
jinja2: 2.8
boto: 2.39.0
pandas_datareader: None
```

Arose from tests in https://github.com/dask/dask/pull/1280
