[IMPR] Make pywikibot.Error more precise
[IMPR] Make pywikibot.Error more precise

- OptionHandler.getOption raises pywikibot.Error if the given option is not
  given in availableOptions. OptionHandler is not used by BaseBot class only
  but also by some generator classes. Make the error message more precise.

Bug: T166982
Change-Id: I011c5d928dba19c7c8f355be19864c56532e52e2

npdoty/pywikibot,happy5214/pywikibot-core,magul/pywikibot-core,wikimedia/pywikibot-core,npdoty/pywikibot,hasteur/g13bot_tools_new,hasteur/g13bot_tools_new,wikimedia/pywikibot-core,PersianWikipedia/pywikibot-core,hasteur/g13bot_tools_new,happy5214/pywikibot-core,magul/pywikibot-core