Raise urllib exception when network error raised.
Raise urllib exception when network error raised.

If there are network problems, the exception should not be caught and
hidden behind a new ParseError without a useful backtrace.

Bug: 66063
Change-Id: I6c2d19a94bcf997f51364efce804ec494274043e

magul/pywikibot-core,h4ck3rm1k3/pywikibot-core,xZise/pywikibot-core,h4ck3rm1k3/pywikibot-core,trishnaguha/pywikibot-core,npdoty/pywikibot,npdoty/pywikibot,hasteur/g13bot_tools_new,VcamX/pywikibot-core,hasteur/g13bot_tools_new,PersianWikipedia/pywikibot-core,wikimedia/pywikibot-core,happy5214/pywikibot-core,jayvdb/pywikibot-core,happy5214/pywikibot-core,Darkdadaah/pywikibot-core,TridevGuha/pywikibot-core,hasteur/g13bot_tools_new,magul/pywikibot-core,emijrp/pywikibot-core,wikimedia/pywikibot-core,icyflame/batman,darthbhyrava/pywikibot-local,Darkdadaah/pywikibot-core,smalyshev/pywikibot-core,valhallasw/pywikibot-core,jayvdb/pywikibot-core