prow/git/git.go
func (r *Repo) MergeCommitsExistBetween(target, head string) (bool, error) {
	r.logger.Infof("Verifying if merge commits exist between %s and %s.", target, head)
	b, err := r.gitCommand("log", fmt.Sprintf("%s..%s", target, head), "--oneline", "--merges").CombinedOutput()
	if err != nil {
		return false, fmt.Errorf("error verifying if merge commits exist between %s and %s: %v. output: %s", target, head, err, string(b))
	}
	return len(b) != 0, nil
}
func (r *Repo) MergeCommitsExistBetween(target, head string) (bool, error) {
	r.logger.Infof("Verifying if merge commits exist between %s and %s.", target, head)
	b, err := r.gitCommand("log", fmt.Sprintf("%s..%s", target, head), "--oneline", "--merges").CombinedOutput()
	if err != nil {
		return false, fmt.Errorf("error verifying if merge commits exist between %s and %s: %v. output: %s", target, head, err, string(b))
	}
	return len(b) != 0, nil
}
// MergeCommitsExistBetween runs 'git log <target>..<head> --merged' to verify
// if merge commits exist between "target" and "head".