Tests that require PRNG are by default seeded from `/dev/urandom`.
However, the user should be able to override with a given seed
to reproduce a failing test.
Instead of messing with command-line arguments, a cleaner approach
is to fetch the seed from an environment variable.
- If the utility library is not built, link to the existing library
when building helper programs for filesystem tests.
- Refactor PRNG seeding in tests.
