Description of problem:

The default `buildah` ClusterBuildStrategy fails if the `Build` or `BuildRun` does not define an output image.

Workaround:

1) Define an output image registry
2) Create a separate BuildStrategy/ClusterBuildStrategy that skips image push

Prerequisites (if any, like setup, operators/versions):

Builds for OpenShift 1.1.0 or Builds for OpenShift 1.2.0

Steps to Reproduce

1. Install Builds for OpenShift 1.1.0 or 1.2.0
2. Create a build using the "buildah" cluster build strategy that does not define an output image (or sets the output image URL to empty)
3. Run the build

Actual results:

Build fails:

[INFO] Pushing image 
Error: invalid image name ""

Expected results:

Image push is skipped

Reproducibility (Always/Intermittent/Only Once):

Always

Acceptance criteria: 

Definition of Done:

Build Details:

Additional info (Such as Logs, Screenshots, etc):