Add option [-V|--version] to emit version string

Add the 'zfs version' and 'zpool version' subcommands to display
the version of the user space utilities and loaded zfs kernel
module.  For example:

$ zfs version
zfs-0.8.0-rc3_169_g67e0366b88
zfs-kmod-0.8.0-rc3_169_g67e0366b88

The '-V' and '--version' aliases were added to support the
common convention of using 'zfs --version` to obtain the version
information.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Richard Laager <rlaager@wiktel.com>
Signed-off-by: TerraTech <1118433+TerraTech@users.noreply.github.com>
Closes #2501
Closes #8567

man/man8/zfs.8

@@ -38,7 +38,7 @@
 .Nd configures ZFS file systems
 .Sh SYNOPSIS
 .Nm
-.Fl ?
+.Fl ?V
 .Nm
 .Cm create
 .Op Fl p
@@ -327,6 +327,8 @@
 .Fl i
 .Op Fl l
 .Ar filesystem
+.Nm
+.Cm version
 .Sh DESCRIPTION
 The
 .Nm
@@ -2453,6 +2455,13 @@ original form.
 Displays a help message.
 .It Xo
 .Nm
+.Fl V, -version
+.Xc
+An alias for the
+.Nm zfs Cm version
+subcommand.
+.It Xo
+.Nm
 .Cm create
 .Op Fl p
 .Oo Fl o Ar property Ns = Ns Ar value Oc Ns ...
@@ -4624,6 +4633,13 @@ Indicates that zfs should make
 inherit the key of its parent. Note that this command can only be run on an
 encryption root that has an encrypted parent.
 .El
+.It Xo
+.Nm
+.Cm version
+.Xc
+Displays the software version of the
+.Nm
+userland utility and the zfs kernel module.
 .El
 .Sh EXIT STATUS
 The

man/man8/zpool.8

@@ -35,7 +35,7 @@
 .Nd configure ZFS storage pools
 .Sh SYNOPSIS
 .Nm
-.Fl ?
+.Fl ?V
 .Nm
 .Cm add
 .Op Fl fgLnP
@@ -210,6 +210,8 @@
 .Cm upgrade
 .Op Fl V Ar version
 .Fl a Ns | Ns Ar pool Ns ...
+.Nm
+.Cm version
 .Sh DESCRIPTION
 The
 .Nm
@@ -933,6 +935,13 @@ The following subcommands are supported:
 Displays a help message.
 .It Xo
 .Nm
+.Fl V, -version
+.Xc
+An alias for the
+.Nm zpool Cm version
+subcommand.
+.It Xo
+.Nm
 .Cm add
 .Op Fl fgLnP
 .Oo Fl o Ar property Ns = Ns Ar value Oc
@@ -2465,6 +2474,13 @@ flag is specified, no features will be enabled on the pool.
 This option can only be used to increase the version number up to the last
 supported legacy version number.
 .El
+.It Xo
+.Nm
+.Cm version
+.Xc
+Displays the software version of the
+.Nm
+userland utility and the zfs kernel module.
 .El
 .Sh EXIT STATUS
 The following exit values are returned: