Fix custom image usage in overrides test (#633)

Author: lfrancke

tests/templates/kuttl/overrides/20-install-druid.yaml.j2

@@ -5,7 +5,12 @@ metadata:
   name: druid
 spec:
   image:
+{% if test_scenario['values']['druid-latest'].find(",") > 0 %}
+    custom: "{{ test_scenario['values']['druid-latest'].split(',')[1] }}"
+    productVersion: "{{ test_scenario['values']['druid-latest'].split(',')[0] }}"
+{% else %}
     productVersion: "{{ test_scenario['values']['druid-latest'] }}"
+{% endif %}
   clusterConfig:
     deepStorage:
       hdfs: