6418 zpool should have a label clearing command

illumos/illumos-gate@6401734d54
6401734d54

https://www.illumos.org/issues/6418
  An easy, direct means of sanitizing pool vdevs can be helpful for management
  purposes.
  FreeBSD has had a 'zpool labelclear' for some time, see: https://
  svnweb.freebsd.org/base?view=revision&revision=224171
  SpectraBSD has a slightly updated version, which I propose for inclusion.

Reviewed by: Yuri Pankov <yuri.pankov@nexenta.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Author: Will Andrews <will@firepipe.net>

Note: the bulk of the change has been already imported, this is a follow
up that imports zpool.1m changes.

man/man1m/zpool.1m

@@ -23,7 +23,7 @@
 .\" Copyright (c) 2013 by Delphix. All rights reserved.
 .\" Copyright 2016 Nexenta Systems, Inc.
 .\"
-.Dd March 25, 2016
+.Dd March 30, 2016
 .Dt ZPOOL 1M
 .Os
 .Sh NAME
@@ -103,6 +103,10 @@
 .Oo Ar pool Oc Ns ...
 .Op Ar interval Op Ar count
 .Nm
+.Cm labelclear
+.Op Fl f
+.Ar device
+.Nm
 .Cm list
 .Op Fl Hpv
 .Op Fl o Ar property Ns Oo , Ns Ar property Oc Ns ...
@@ -1154,6 +1158,21 @@ pool, in addition to the pool-wide statistics.
 .El
 .It Xo
 .Nm
+.Cm labelclear
+.Op Fl f
+.Ar device
+.Xc
+Removes ZFS label information from the specified
+.Ar device .
+The
+.Ar device
+must not be part of an active pool configuration.
+.Bl -tag -width Ds
+.It Fl f
+Treat exported or foreign devices as inactive.
+.El
+.It Xo
+.Nm
 .Cm list
 .Op Fl Hpv
 .Op Fl o Ar property Ns Oo , Ns Ar property Oc Ns ...