Yeah uh, I don't think `$shell` is ever set in the functional1
environment. Pretty sure this has been expanding to `''` THIS WHOLE
TIME.
Also `SHELL` is `/sbin/nologin` in that builder. idk why so I'm just
passing `shell` unconditionally in functional's `mkDerivation` helper.
Maybe next we should put `set -euo pipefail` into all these test
builders?
Change-Id: Ie5fb85305932c03a901ba84ffcce48f16a6a6964
Qyriad
0d3fdbdb54