BUG: read_excel() fails when checking __version__ of older xlrd versions
- [X] I have checked that this issue has not already been reported.

- [X] I have confirmed this bug exists on the latest version of pandas.

- [ ] (optional) I have confirmed this bug exists on the master branch of pandas.

---

#### When xlrd is installed but is an "older" version (e.g. 1.1.0):

```python
pandas.read_excel("file.xlsx", engine="openpyxl")
```

raises

```python
AttributeError: module 'xlrd' has no attribute '__version__'
```

This specifically occurs in ``pandas/io/excel/_base.py:336``

#### Problem description

This bug occurs regardless of the ``engine`` input because ``pandas.read_excel()`` _always_ checks ``xlrd.__version__`` if any version of xlrd is installed. Older versions of xlrd use ``__VERSION__`` instead of ``__version__`` instead, which results in the AttributeError.

This exception does not occur and everything behaves as expected if:

- xlrd is not installed
- A "newer" version of xlrd is installed (that has the ``__version__`` attribute)


#### Expected Output

According to the documentation, 
```
Changed in version 1.2.0: When engine=None, the following logic will be used to determine the engine:
    
- If path_or_buffer is an OpenDocument format (.odf, .ods, .odt), then odf will be used.
- Otherwise if path_or_buffer is an xls format, xlrd will be used.
- Otherwise if openpyxl is installed, then openpyxl will be used.
- Otherwise if xlrd >= 2.0 is installed, a ValueError will be raised.
- Otherwise xlrd will be used and a FutureWarning will be raised. This case will raise a ValueError in a future version of pandas.

```

Based on this, I believe the intended behavior is:
- read_excel() should _not_ check the xlrd version if engine is ``"openpyxl"``
- If read_excel() does need to know the version of xlrd, it should try both ``__version__`` and ``__VERSION__``

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

<details>

INSTALLED VERSIONS
------------------
commit           : 3e89b4c4b1580aa890023fc550774e63d499da25
python           : 3.7.4.final.0
python-bits      : 64
OS               : Linux
OS-release       : 3.10.0-1062.4.1.el7.x86_64
Version          : #1 SMP Wed Sep 25 09:42:57 EDT 2019
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : en_US
LOCALE           : en_US.ISO8859-1

pandas           : 1.2.0
numpy            : 1.19.1
pytz             : 2020.1
dateutil         : 2.8.1
pip              : 20.3.3
setuptools       : 40.8.0
Cython           : None
pytest           : 6.0.1
hypothesis       : None
sphinx           : 3.2.1
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : 2.11.2
IPython          : 7.19.0
pandas_datareader: None
bs4              : None
bottleneck       : None
fsspec           : None
fastparquet      : None
gcsfs            : None
matplotlib       : 3.3.2
numexpr          : 2.7.1
odfpy            : None
openpyxl         : 3.0.5
pandas_gbq       : None
pyarrow          : None
pyxlsb           : None
s3fs             : None
scipy            : 1.5.2
sqlalchemy       : None
tables           : 3.6.1
tabulate         : 0.8.7
xarray           : None
xlrd             : 1.1.0
xlwt             : None
numba            : None


</details>
