Bug 65145: do not run generate_user_files if stdout is a pipe
Bug 65145: do not run generate_user_files if stdout is a pipe

pip will run generate_user_files with stdout directed to a log
file, but stdin as a terminal. As such, GUF will wait for user
input, but the user has no idea they should input anything.
This change prevents that.

Change-Id: Iaa596bf40e4d49c73b9a73ee6423c3a6b6899449

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