Revise the disabling of broad-except pylint warning (W0703)

[sechkova]

Description of issue or feature request:
An (anti)pattern starts to appear in the newer code (where stricter pylint checks are applied), a tendency to disable broad-except warnings.

Even though each case has its arguments, we should as a minimum make sure we log the exception and not silently bury it.

Current behavior:
# pylint: disable=broad-except throughout the code

Expected behavior:
At least log the exception before ignoring it:

try:
    do_something()
except Exception as e:
    logger.exception("An exception occurred")

Sync with #1178

[sechkova]

This issue is directly related to the newer parts of code (api/*) where the new api/pylintrc config applies:

tuf/api/serialization/json.py:        except Exception as e:  # pylint: disable=broad-except
tuf/api/serialization/json.py:        except Exception as e:  # pylint: disable=broad-except
tuf/api/serialization/json.py:        except Exception as e:  # pylint: disable=broad-except

In the top-level pylintrc used by the rest of the code the broad-except warning is disabled globally.

[jku]

It's possible that the deserialization cases are actually appropriate (I'm not sure if we can figure out all the ways that deserialization can fail, and the callers certainly won't care too much) but you are right we should review this.

[sechkova]

I tested this with the intention to close the issue since the disable is well justified in serialisation/json.py and another exception is re-raised from the broad one ... but surprisingly pylint agrees with us!
Pylint does not emit the error anymore and the disabling is not needed ... it was needed when python 2.x was supported and six was used (see bd94f6d).

Assigning this to myself to fix it (remove the disabling of the warning).