cp's -T and --reflink=auto are only available on GNU coreutils

Docker-DCO-1.1-Signed-off-by: Kato Kazuyoshi <kato.kazuyoshi@gmail.com> (github: kzys)
Merge pull request #6643 from kzys/freebsd-cp

cp's -T and --reflink=auto are only available on GNU coreutils