lastcomm: update i386 tests for additional timestamp resolution

Fixes: 6f4ce7e89ba4 ("lastcomm: improve timestamp display")
Sponsored by: The FreeBSD Foundation

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.

Differential Revision: https://reviews.freebsd.org/D7079 (as part of a larger diff)
MFC after: 1 week
PR: 210329
Reported by: asomers
Approved by: re (gjb)
Reviewed by: cem
Sponsored by: EMC / Isilon Storage Division

Migrate tools/regression/{usr.bin/lastcomm,usr.sbin}/ to the new tests layout.

This change was originally going to only migrate the usr.sbin tests but, as
it turns out, the usr.sbin/sa/ tests require files from usr.bin/lastcomm/
so it's better to just also migrate the latter at the same time. The other
usr.bin tests will be moved separately.

To make these tests work within the test suite, some of them have required
changes to prevent modifying the source directory and instead just rely on
the current directory for file manipulation.