ZTS: Written props test fails with 4k disks

With 4k disks, this test will fail in the last section because the
expected human readable value of 20.0M is reported as 20.1M. Rather than
use the human readable property, switch to the parsable property and
verify that the values are reasonably close.

Reviewed-by: Igor Kozhukhov <[email protected]>
Reviewed-by: Ryan Moeller <[email protected]>
Reviewed-by: Tony Hutter <[email protected]>
Signed-off-by: John Kennedy <[email protected]>
Closes #9477

tests/zfs-tests/tests/functional/cli_root/zfs_property/zfs_written_property_001_pos.ksh

@@ -11,7 +11,7 @@
 #
 
 #
-# Copyright (c) 2012, 2016 by Delphix. All rights reserved.
+# Copyright (c) 2012, 2017 by Delphix. All rights reserved.
 #
 
 #
@@ -216,15 +216,15 @@ for ds in $datasets; do
 	    count=$blocks
 	sync_pool
 done
-recursive_output=$(zfs get -r written@current $TESTPOOL | \
+recursive_output=$(zfs get -p -r written@current $TESTPOOL | \
     grep -v $TESTFS1@ | grep -v $TESTFS2@ | grep -v $TESTFS3@ | \
     grep -v "VALUE" | grep -v "-")
-expected="20.0M"
+expected="$((20 * mb_block))"
 for ds in $datasets; do
 	writtenat=$(echo "$recursive_output" | grep -v $ds/)
 	writtenat=$(echo "$writtenat" | grep $ds | awk '{print $3}')
-	[[ $writtenat == $expected ]] || \
-	    log_fail "recursive written property output mismatch"
+	within_percent $writtenat $expected 99.5 || \
+	    log_fail "Unexpected written@ value on $ds"
 done
 
 log_pass "zfs written and written@ property fields print correct values"