Setup.pm: specify NIX_ env vars for running yath

Dependencies

• [2] U2PHPVGD t/Setup.pm: sort NIX_ env vars
• [*] HX4QYOYA add first evaluations tests
• [*] UIA3ULNU Give each test its own Nix directories

Change contents

• edit in t/lib/Setup.pm at line 59
  [2.50]

  [5.1894]
  + $ENV{'NIX_REMOTE_SYSTEMS'} = '';

  + $ENV{'NIX_REMOTE'} = '';