Unable to read number_format with pandas / openpyxl (engine)
#### Code Sample

```python
# Your code here
import pandas as pd
data = pd.read_excel('temp.xlsx', engine="openpyxl")
print(data.iloc[0][4].number_format)

######Via openpyxl
from openpyxl import load_workbook
wb = load_workbook('temp.xlsx')
ws = wb.worksheets[0]

col_d = ws.cell(row=2, column=5)
print(col_d.value)
col_nf = col_d.number_format
print(col_nf)

```

#### Problem description

Unable to access number_format in pandas dataframe using engine openpyxl. 
But i am able to acccess the number_format in plain openoyxl via above code.



#### Expected Output
"$"#,##0
#### Output of ``pd.show_versions()``

<details>

[paste the output of ``pd.show_versions()`` here below this line]
INSTALLED VERSIONS
------------------
commit           : None
python           : 3.6.8.final.0
python-bits      : 64
OS               : Windows
OS-release       : 10
machine          : AMD64
processor        : Intel64 Family 6 Model 142 Stepping 9, GenuineIntel
byteorder        : little
LC_ALL           : None
LANG             : None
LOCALE           : None.None

pandas           : 0.25.2
numpy            : 1.17.3
pytz             : 2019.2
dateutil         : 2.8.0
pip              : 19.3.1
setuptools       : 41.6.0
Cython           : None
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : 0.9.3
psycopg2         : None
jinja2           : None
IPython          : None
pandas_datareader: None
bs4              : None
bottleneck       : None
fastparquet      : None
gcsfs            : None
lxml.etree       : None
matplotlib       : None
numexpr          : None
odfpy            : None
openpyxl         : 3.0.2
pandas_gbq       : None
pyarrow          : None
pytables         : None
s3fs             : None
scipy            : None
sqlalchemy       : 1.3.10
tables           : None
xarray           : None
xlrd             : 1.2.0
xlwt             : None
xlsxwriter       : None
None

</details>
