* Touch up string expansion.
I'm chasing this:
```
$ (module purge; spack install perl %gcc/5.4.0)
==> Error: No installed spec matches the hash: '%s'
```
There's something deeper going on, but the error message isn't helpful.
After this change it tells me this:
```
$ (module purge; spack install perl %gcc/5.4.0)
==> Error: No installed spec matches the hash: '5.4.0'
```
Which is weird because `5.4.0` is not a hash... Whatever is going on here, the error message needs to be fixed.
* Flake8 whitespace
26440accab