Fix "unbound variable" for Spark plugin
Fix "unbound variable" for Spark plugin

We can't create Spark image,
has error "JAVA_DOWNLOAD_FILE: unbound variable"

Change-Id: I92105f55f9980cc0dca40c78e9b21fb52a36689e
Closes-bug: #1441593

crobby/sahara-image-elements,uladz/sahara-image-elements,openstack/sahara-image-elements,bigfootproject/sahara-image-elements,crobby/sahara-image-elements,bigfootproject/sahara-image-elements,openstack/sahara-image-elements,uladz/sahara-image-elements