Fix .../usr.bin/lastcomm/legacy_test:main on i386
The time in the output files was ahead by 3 hours on i386. Fix the incorrect
offset.
While here, make a minor change to output the diffs to standard error so the
issues with the results are apparent when running kyua debug,
kyua report-html, etc.
MFC after: 1 week
PR: 210329
Reported by: asomers
Sponsored by: EMC / Isilon Storage Division