dc78f4c58a
* environment.py: allow link:run
Some users want minimal views, excluding run-type dependencies, since
those type of dependencies are covered by rpaths and the symlinked
libraries in the view aren't used anyways.
With this change, an environment like this:
```
spack:
specs: ['py-flake8']
view:
default:
root: view
link: run
```
includes python packages and python, but no link type deps of python.