[cleanup] Use suggest_help to suggest help in transferbot.py
[cleanup] Use suggest_help to suggest help in transferbot.py

Use commonly used suggest_help instead of exception handling

Change-Id: Ie60c617d26696079c86560abcdab726f011568d4

PersianWikipedia/pywikibot-core,wikimedia/pywikibot-core,wikimedia/pywikibot-core