[IMPROV] Thread tests: Simplified intersections
[IMPROV] Thread tests: Simplified intersections

Instead of using itertools.product it is using sets and their
'intersection' method.

Change-Id: I162573d122e09aba2b3dd0f2a12f78fb2b3018bf

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