Demote the whackbang in the zpool_id script.

The zpool_id script is posixly correct and does not use bash
features, so change its whackbang from /bin/bash to /bin/sh.

Debian policy also stipulates that system scripts be dash compatible.

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

cmd/zpool_id/zpool_id

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/bin/sh
 
 CONFIG="${CONFIG:-/etc/zfs/zdev.conf}"
 AWK="${AWK:-/usr/bin/awk}"