bug 876159 - set self.return_code since buildbot truncates logs. r=philor
bug 876159 - set self.return_code since buildbot truncates logs. r=philor

--HG--
branch : production
extra : transplant_source : %D9%0A%AD9%AC%1Ft%CA%CF%F9%3B%FCrU%8FZ%CE%DC%FC%F2

walac/build-mozharness,mrrrgn/build-mozharness,lundjordan/mozharness,kartikgupta0909/mozilla-mozharness,armenzg/build-mozharness,kartikgupta0909/mozilla-mozharness,kartikgupta0909/gittest,lundjordan/mozharness,escapewindow/mozharness,armenzg/build-mozharness,escapewindow/mozharness,simar7/build-mozharness,mrrrgn/build-mozharness,simar7/build-mozharness,kartikgupta0909/gittest,kartikgupta0909/build-mozharness,mozilla/build-mozharness,lissyx/build-mozharness,mozilla/build-mozharness,lissyx/build-mozharness,walac/build-mozharness,kartikgupta0909/build-mozharness