Intentionally Fail a DAG

Maybe I'm just missing something in the documentation, but my use case is that I want there to be a check in my DAG for a specific condition and if that condition fails, for the whole DAG to be marked as a failure. The `preconditions` attribute on the steps helps with the first part of only executing when a condition is satisfied, but I'm having trouble figuring out how to then mark the DAG as a failure. If I simply check for the positive condition and it comes back as negative, the rest of the steps don't execute, but the DAG is marked as finished successfully. I tried adding a branch for the negative condition, but I can't figure out how to make the DAG show as failed. I thought setting the `signalOnStop` for the negative condition step to something like "SIGQUIT" would do it, but it still comes through as "finished".
A simple DAG to reproduce looks like this.
```yaml
params: foo
steps:
- name: step1
command: "echo $1"
- name: positive case
depends:
- step1
preconditions:
- condition: "$1"
expected: "foo"
command: "echo 'Success'"
- name: negative case
depends:
- step1
preconditions:
- condition: "$1"
expected: "bar"
command: "echo 'Failure'"
signalOnStop: "SIGQUIT"
```