Jenkinsfile: Correctly set pipeline status on a build failure.

Otherwise the pipeline cannot be meaningfully used as a validation
job, as it'd always return success, even upon encountering one or more
build failures.

* Jenkinsfile: In case a packaging target failed building, set the
build result to failure.

Change-Id: I47c8b09936b088b27a02173aa94a0adb0f04dcb4