ZTS: use openssl for md5digest and sha256digest

On larger files this should improve the speed.

Sample values of my system:

[mcmilk@xz]$ time dd if=/dev/zero bs=128k count=1k | sha256sum
254bcc3fc4f27172636df4bf32de9f107f620d559b20d760197e452b97453917 -
real 0m1,050s
user 0m0,985s
sys 0m0,153s

[mcmilk@xz]$ time dd if=/dev/zero bs=128k count=1k | openssl sha256 -r
254bcc3fc4f27172636df4bf32de9f107f620d559b20d760197e452b97453917 *stdin
real 0m0,254s
user 0m0,206s
sys 0m0,160s

I think cli_root/zdb/zdb_backup.ksh runs also an FreeBSD and I needed to
include the sysutils/coreutils package for the FreeBSD tests within the
QEMU patchset.

This could be reverted, when this pull request gets upstream

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tino Reichardt <milky-zfs@mcmilk.de>
Closes #16543