write unit test on environment variable and attribute substitution for action parameters

[HenryGeorgist]

https://github.com/USACE/cc-java-sdk/blob/158630e47049eef228912de9c2d11840b7e725ee/src/main/java/usace/cc/plugin/api/PluginManager.java#L115

usage with existing plugins has indicated that action attribute substitution is not picking up env variables. The debugging session i went through indicated that while the substitution happens the original entryset is not updated, it seems like val is not a reference.