archive: tests and benchmarks for hardlinks

adding moar infomation, so benchmark camparisons can be moar
comparitive.

This is a part of the commits in #8046, but is usable in master for test and comparison.

ping  @tiborvass  @unclejack 

Signed-off-by: Vincent Batts <vbatts@redhat.com>
If this is an utility function, it shouldn't deal with `t *testing.T`.