CircleCI errors rather than timeouts if bg task fails

Previously if Sauce Connect or the screenshots script failed, they
wouldn't touch the readyfile and our while loops waiting on the
readyfiles would time out, even though neither Sauce Connect nor the
screenshots script were hanging, they just didn't notify us of their
failure.

Now they notify us of failure by writing 'ERROR' to their readyfiles,
which our while loops test for.
1 file changed