CI fails if a pull request is behind the tip of master

[jbarrick-mesosphere]

What happened:

My PR was behind the tip of master and so CI fails with a cryptic error: https://circleci.com/gh/kudobuilder/kudo/451?utm_campaign=vcs-integration-link&utm_medium=referral&utm_source=github-build-link

#!/bin/bash -eo pipefail
git merge origin/master


*** Please tell me who you are.

Run

  git config --global user.email "you@example.com"
  git config --global user.name "Your Name"

to set your account's default identity.
Omit --global to set the identity only in this repository.

fatal: unable to auto-detect email address (got 'root@b16b0e0b495e.(none)')
Exited with code 128

What you expected to happen:

CI should either pass, or give an error indicating I should rebase.

How to reproduce it (as minimally and precisely as possible):

git fetch origin master
git checkout -b ci-fail
git reset --hard origin/master^1
echo hello > keps/draft-ci-fail.md
git add keps/draft-ci-fail.md
git commit -m 'a commit'
git push $remote ci-fail