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

tests/zfs-tests/include/libtest.shlib

@@ -3460,18 +3460,7 @@ function tunable_exists
 #
 function md5digest
 {
-	typeset file=$1
-
-	case "$UNAME" in
-	FreeBSD)
-		md5 -q $file
-		;;
-	*)
-		typeset sum _
-		read -r sum _ < <(md5sum -b $file)
-		echo $sum
-		;;
-	esac
+	openssl md5 -r $1 | awk '{print $1}'
 }
 
 #
@@ -3492,18 +3481,7 @@ function cmp_md5s {
 #
 function sha256digest
 {
-	typeset file=$1
-
-	case "$UNAME" in
-	FreeBSD)
-		sha256 -q $file
-		;;
-	*)
-		typeset sum _
-		read -r sum _ < <(sha256sum -b $file)
-		echo $sum
-		;;
-	esac
+	openssl sha256 -r $1 | awk '{print $1}'
 }
 
 function new_fs #<args>