Variable resolution order

All variables in the file are resolved in the following specific order:

• Preset Variables based on command line entered.

• Derived Variables in the order they appear in the DockMaker.properties file. Derived Variables only have access to Preset Variables and any Derived Variables that appear earlier in the file.

• Mandatory variables and their dependencies just before applying that variable.

Other variables can be added as necessary to simplify the definition process. For example, docker.download.host.prefix was added to facilitate the hostname in the URLs.