Use Spec.format for token substitution in modules (#1848)

This replaces a custom token-based substitution format with calls to
Spec.format in modules.py

This also resolves a couple issues:

- LmodModules set configuration globally instead of in its initializer
  which meant test-specific configuration was not applied
- Added support for setting hash_length=0 for LmodModules. This only
  affects the module filename and not the directory names for the
  hierarchy tokens in the path. This includes an additional unit test.