back off harder when config.sh fails r=aki
back off harder when config.sh fails r=aki

seeing if this helps with the load spikes on git.mozilla.org (e.g. bug 990311)

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