Merge pull request #92 from Ouranosinc/ignore-optional-artifact

## Changes

- Adds check to avoid error on missing `buildout/*.output.ipynb` to archive artifact.

## Related Issue / Discussion

- Resolves bird-house/birdhouse-deploy#220 (comment)
- Fix regression from #91

Jenkinsfile

@@ -120,7 +120,7 @@ Note this is another run, will double the time and no guaranty to have same erro
             archiveArtifacts(artifacts: 'raven-*/docs/source/notebooks/*.ipynb', fingerprint: true)
             archiveArtifacts(artifacts: 'esgf-compute-api-*/examples/*.ipynb', fingerprint: true)
             archiveArtifacts(artifacts: 'PAVICS-landing-*/content/notebooks/climate_indicators/*.ipynb', fingerprint: true)
-            archiveArtifacts(artifacts: 'buildout/*.output.ipynb', fingerprint: true)
+            archiveArtifacts(artifacts: 'buildout/*.output.ipynb', fingerprint: true, allowEmptyArchive: true)
             archiveArtifacts(artifacts: 'buildout/env-dump/', fingerprint: true)
         }
 	unsuccessful {  // Run if the current builds status is "Aborted", "Failure" or "Unstable"