WIP (PUP-3162) Issue/stable/pup 3162 block environment interpolation

Here's a first pass at blocking interpolation of $environment in environment related settings when using directory environments.  It currently logs an error and prevents interpolation for

* environmentpath
* basemodulepath
* default_manifest
* environment

There are several open questions that need to be sorted out before this is merged.

1.  What to do with modulepath/manifest, and whether default_manifest should follow with them.
2. Fail completely (as PUP-3069 does for default_manifest) or not interpolate $environment, log warning, and continue as this patch currently does (except for default_manifest...)
3. Other settings I missed?

I've written them up in more detail in PUP-3162 for discussion.