ZTS: Cleanup partition tables

The cleanup_devices function should remove any partitions created
on the device and force the partition table to be reread.  This
is needed to ensure that blkid has an up to date version of what
devices and partitions are used by zfs.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

tests/zfs-tests/include/libtest.shlib

@@ -2301,10 +2301,11 @@ function cleanup_devices #vdevs
 {
 	typeset pool="foopool$$"
 
-	if poolexists $pool ; then
-		destroy_pool $pool
-	fi
+	for vdev in $@; do
+		zero_partitions $vdev
+	done
 
+	poolexists $pool && destroy_pool $pool
 	create_pool $pool $@
 	destroy_pool $pool