emailext default subject/body don't apply to pipeline jobs

Change-Id: I449e606fc785f90d684567e149f7fdb9a10d770e
diff --git a/jjb/pipeline/imagebuilder.groovy b/jjb/pipeline/imagebuilder.groovy
index a8636ea..1d5a950 100644
--- a/jjb/pipeline/imagebuilder.groovy
+++ b/jjb/pipeline/imagebuilder.groovy
@@ -77,6 +77,8 @@
     }
     failure {
       emailext (
+        subject: "$PROJECT_NAME - Build # $BUILD_NUMBER - $BUILD_STATUS",
+        body: "Check console output at $BUILD_URL to view the results.",
         to: "${params.failureEmail}"
       )
     }