Fix loop in Dracut shutdown script

The shell executes each command of a pipeline in a subshell,
thus $ret always had the same value after the while loop that
it had before the loop (http://mywiki.wooledge.org/BashFAQ/024),
signaling success even if some of the zpools could not be exported.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #3083

dracut/90zfs/export-zfs.sh.in

@@ -10,7 +10,7 @@ _do_zpool_export() {
 	fi
 
 	info "Exporting ZFS storage pools"
-	zpool list -H | while read fs rest ; do
+	for fs in `zpool list -H -o name` ; do
 		zpool export $force "$fs" || ret=$?
 	done