Replace bare excepts by explicit excepts in pandas/tests/
(superseeds #18419, same task for different files: #22873, #22874, #22875, #22877)

In several parts of the code, we have bare excepts in the form of:
```python
try:
    my_value = my_dict[my_key]
except:  # we are capturing all the exceptions, when we want to capture only KeyError
    my_value = None
```

This is a bad practice, and we want to avoid having this in the code. What we want instead is:
```python
try:
    my_value = my_dict[my_key]
except KeyError:
    my_value = None
```
Of course in every case, the exception can be different (not always `KeyError`), and some research is needed to see which is the right exception (or exceptions, it can be a tuple) that needs to be captured. In some cases, every exception needs to be captured and we'll use `except Exception:`, but this should be avoided unless we really need to capture all exceptions.

This issue is to fix all the bare excepts in testing files `pandas/tests/`. At the moment they are (note that the list can change as code evolves):
```
pandas/tests/test_multilevel.py:1378:9: E722 do not use bare except'
pandas/tests/test_nanops.py:144:9: E722 do not use bare except'
pandas/tests/test_nanops.py:149:9: E722 do not use bare except'
pandas/tests/test_nanops.py:170:21: E722 do not use bare except'
pandas/tests/test_nanops.py:174:21: E722 do not use bare except'
pandas/tests/test_panel.py:338:13: E722 do not use bare except'
pandas/tests/test_panel.py:344:13: E722 do not use bare except'
pandas/tests/test_strings.py:2663:13: E722 do not use bare except'
pandas/tests/indexing/common.py:154:13: E722 do not use bare except'
pandas/tests/indexing/common.py:217:17: E722 do not use bare except'
pandas/tests/io/test_pytables.py:54:9: E722 do not use bare except'
pandas/tests/io/test_pytables.py:62:5: E722 do not use bare except'
pandas/tests/io/test_pytables.py:120:5: E722 do not use bare except'
pandas/tests/io/test_pytables.py:4624:21: E722 do not use bare except'
pandas/tests/io/test_sql.py:1793:9: E722 do not use bare except'
pandas/tests/io/test_sql.py:2378:9: E722 do not use bare except'
pandas/tests/io/test_sql.py:2405:9: E722 do not use bare except'
pandas/tests/io/formats/test_format.py:73:5: E722 do not use bare except'
pandas/tests/io/formats/test_format.py:455:13: E722 do not use bare except'
```
An updated list can be obtained by running: `flake8 --select=E722 --config=none pandas/tests/`