Previously the runner was returning "1" on success and "0" on failure.
Swap this so that it correctly returns "0" on success and "1" on fail.
This only affected "--bot-mode" which isn't yet enabled.

Bug: angleproject:3162
Change-Id: I1ee942223272d24eff137279d5a0638d3a65694e
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2419639Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>