fix job def output value

Author: wleepang

src/templates/_common/container-build.template.yaml

@@ -450,7 +450,7 @@ Outputs:
       Fn::If:
       - CreateBatchJobDefinitionTrue
       - !Ref BatchJobDef
-      - ""
+      - "-"
     Export:
       Name: !Sub ${AWS::StackName}-BatchJobDefinition