Handle SSH launcher not being exported by JCasC

[timja]

• Handle SSH launcher not being exported by JCasC
• Handle null init script (as jelly submits empty string and JCasC does null)
• Create a node properties list copy so we don't accidentally add the FQDN variable to the template

Fixes #567

I wasn't able to figure out why it wasn't being exported, would need to refresh myself on this area of jcasc code and it would take a lot more effort than this simple patch

Testing done

Tested without providing a launcher in jcasc and it now works

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