Add exit code for Application::doRun()
Add exit code for Application::doRun()

Symfony console application expected that method doRun() will return an exit code: zero if everything went fine, or an error code.
It prevents `The command terminated with an error status ()` error after every command in console.
karmazzin/DrupalConsole,Cottser/DrupalConsole,reszli/DrupalConsole,reszli/DrupalConsole,reszli/DrupalConsole,Cottser/DrupalConsole,AniRai/DrupalConsole,revagomes/DrupalConsole,revagomes/DrupalConsole,karmazzin/DrupalConsole,revagomes/DrupalConsole,dkgndec/DrupalConsole,alxvallejo/DrupalConsole,Cottser/DrupalConsole,karmazzin/DrupalConsole,AniRai/DrupalConsole,dkgndec/DrupalConsole,frega/DrupalConsole,frega/DrupalConsole,dkgndec/DrupalConsole,alxvallejo/DrupalConsole,AniRai/DrupalConsole,frega/DrupalConsole,alxvallejo/DrupalConsole