Fix return value of generator on non-ostree systems

[cgwalters]

Commit aa72caf
regressed the ostree-system-generator on non-ostree systems. If there's no ostree= karg, we need to just exit 0.

Closes: #2909
Fixes: aa72caf

[ericcurtin]

LGTM, responding on phone. Had not noticed this regression, apologies.

[dbnicholson]

I don't know what to make of the kola failure. I can't tell if it's transient or related to this change.

[cgwalters]

I think that's just an instance of a low-frequency flake we've seen; #2912 will help a little in debugging it hopefully.

[cgwalters]

Flaked on coreos/fedora-coreos-tracker#1511
/override continuous-integration/jenkins/pr-merge

[openshift-ci]

@cgwalters: Overrode contexts on behalf of cgwalters: continuous-integration/jenkins/pr-merge

In response to this:

Flaked on coreos/fedora-coreos-tracker#1511
/override continuous-integration/jenkins/pr-merge

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[ericcurtin]

This still fails in the Android Boot case, because this regex basically doesn't apply:

regex = g_regex_new ("^/ostree/boot.[01]/([^/]+)/", 0, 0, NULL);

but I'm gonna fix it up.