Optionally allow empty junit test results

Change-Id: Ic0f8f939e32bdbc2bf264e0386cb97489877aacb
diff --git a/jjb/python-unit.yaml b/jjb/python-unit.yaml
index e035f45..a11b533 100644
--- a/jjb/python-unit.yaml
+++ b/jjb/python-unit.yaml
@@ -67,6 +67,7 @@
     publishers:
       - junit:
           results: "**/*junit.xml,**/*results.xml,**/*report.xml"
+          allow-empty-results: '{junit-allow-empty-results}'
       - cobertura:
           report-file: "**/*coverage.xml"
           targets: