logging: Report stack_info on logging.exception calls.

The exception trace only goes from where the exception was thrown up
to where the `logging.exception` call is; any context as to where
_that_ was called from is lost, unless `stack_info` is passed as well.
Having the stack is particularly useful for Sentry exceptions, which
gain the full stack trace.

Add `stack_info=True` on all `logging.exception` calls with a
non-trivial stack; we omit `wsgi.py`.  Adjusts tests to match.

zerver/views/zephyr.py

@@ -63,7 +63,7 @@ def webathena_kerberos_login(request: HttpRequest, user_profile: UserProfile,
                                api_key,
                                base64.b64encode(ccache).decode("utf-8")])
     except Exception:
-        logging.exception("Error updating the user's ccache")
+        logging.exception("Error updating the user's ccache", stack_info=True)
         return json_error(_("We were unable to setup mirroring for you"))
 
     return json_success()