Fix exception logging

[apriltuesday]

The current logging results in cryptic NoneType: None error messages, due to the fact that logger.exception does not work outside a handler / except clause (see here).

>>> def f():
...     raise ValueError('bad thing')
>>> try:
...     f()
... except Exception as e:
...     caught = e
>>> logger.exception(caught)

bad thing
NoneType: None

>>> try:
...    f()
... except Exception as e:
...     logger.exception(e)
    
bad thing
Traceback (most recent call last):
  File "<input>", line 2, in <module>
  File "<input>", line 2, in f
ValueError: bad thing

I don't think we need both the print and the logger.exception, but we can change it if desired.

[tcezard]

Makes sense. Alternatively we could format and write the stack trace ourselves if we didn't want to repeat the logger.exception statement too many times:

import traceback
traceback.format_exc(caught_exception)