Backport: vdev_id-use-mawk-compatible-regular-expression.patch

Commit: zfsonlinux/zfs@2d9d57b0fbe17b56a1bdd09505400144778cb189
From: Ned Bass <bass6@llnl.gov>
Date: Wed, 17 Dec 2014 11:01:42 -0800
Subject: vdev_id: use mawk-compatible regular expression

Slot mapping in vdev_id doesn't work on systems using mawk as the 'awk'
alternative. A regular expression in map_slot() contains an unquoted
empty string following the alternation (|) operator, which results in an
"missing operand" error with mawk. The solution is to rearrange the
expression so the alternation has two operands.

Signed-off-by: Ned Bass <bass6@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes zfsonlinux/pkg-zfs#136
Closes zfsonlinux/zfs#2965