nixos/nix-daemon: assert system or systems for buildMachines.

Commit 5395397f removed the assertions from the buildMachines to
ensure that either system or systems is set for each buildmachine.

This patch re-implements those assertions.

The symptom is that if both system and systems are omitted, then the
/etc/machines file has the wrong number of columns and any attempt to
run a `nix` operation that has to perform a build will fail with a
`strtoull` exception.

0 files changed, 0 insertions, 0 deletions