Raise RuntimeError instead of using the nonexistent self.error
Raise RuntimeError instead of using the nonexistent self.error

Fixes #136.

lundjordan/build-relengapi,Callek/build-relengapi,srfraser/services,La0/mozilla-relengapi,Callek/build-relengapi,lundjordan/build-relengapi,garbas/mozilla-releng-services,lundjordan/services,djmitche/build-relengapi,djmitche/build-relengapi,hwine/build-relengapi,srfraser/services,lundjordan/services,djmitche/build-relengapi,La0/mozilla-relengapi,La0/mozilla-relengapi,Callek/build-relengapi,mozilla-releng/services,lundjordan/services,mozilla/build-relengapi,mozilla/build-relengapi,mozilla/build-relengapi,mozilla/build-relengapi,hwine/build-relengapi,Callek/build-relengapi,lundjordan/build-relengapi,garbas/mozilla-releng-services,djmitche/build-relengapi,srfraser/services,andrei987/services,garbas/mozilla-releng-services,andrei987/services,lundjordan/services,La0/mozilla-relengapi,lundjordan/build-relengapi,andrei987/services,hwine/build-relengapi,mozilla-releng/services,mozilla-releng/services,srfraser/services,garbas/mozilla-releng-services,andrei987/services,hwine/build-relengapi,mozilla-releng/services