Add variable substitution in ApplicationManifestUtils

[luschmar]

Add functionality Variables to a Manifest in ApplicationManifestUtils

[linux-foundation-easycla]

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• ✅ login: luschmar (073c85c, 5ed5eea)

[dmikusa]

Thanks for adding the additional tests.

I do think this should error/throw an exception though if an env variable is not substituted. It would be consistent with the cf cli behavior, which is I think what we should strive for with the operations library (it's higher level).

> cf push
Expected to find variables: foo
FAILED

It may not be specifically listed as invalid to have an app name including ((foo)) but the flip side is that if you have an env variable set and accidentally forget to set it to something that could have ramifications as well. Maybe you push the app with the wrong name or wrong route or wrong service bound. It's safer to throw an error/exception and let the user handle that.

You as a user could simply catch that exception and ignore it, if you don't care, but you can't do the opposite.

[dmikusa]

Thanks @luschmar !