Make sure, that vtysh_cmd.c is deterministically generated.

--- a/vtysh/extract.pl.in	2017-03-10 13:55:06.000000000 +0100
+++ b/vtysh/extract.pl.in	2017-06-24 00:51:56.460000000 +0200
@@ -214,7 +214,7 @@
 }
 
 # Output DEFSH
-foreach (keys %live) {
+foreach (sort keys %live) {
     my ($proto);
     my ($key);
     $key = $live{$_};
@@ -229,7 +229,7 @@
 {
 EOF
 
-foreach (keys %odefun) {
+foreach (sort keys %odefun) {
     my ($node, $str) = (split (/,/));
     $cmd = $ocmd{$_};
     $cmd =~ s/_cmd/_cmd_vtysh/;
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<div class='path'>path: <a href='/guix/log/?id=63102406f22412bb922de5549deb89d3594a38c0'>root</a>/<a href='/guix/log/ROADMAP?id=63102406f22412bb922de5549deb89d3594a38c0'>ROADMAP</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/ROADMAP?id=63102406f22412bb922de5549deb89d3594a38c0&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2016-01-29 20:21:54 +0300'>2016-01-29</span></td><td><a href='/guix/commit/ROADMAP?id=171a0a13a4350ac9bbed0f2ed8e9c9777cc57b22'>Rename 'dmd' to 'shepherd' in comments and strings.</a><span class='msg-avail'>...<span class='msg-tooltip'>* build-aux/hydra/demo-os.scm (operating-system)[issue]: Point to
  shepherd instead of dmd.
* ROADMAP: Likewise.
* gnu/build/install.scm (directives): Adjust comment.
</span></span></td><td>Alex Kost</td></tr>
<tr><td><span title='2015-01-22 22:52:11 +0100'>2015-01-22</span></td><td><a href='/guix/commit/ROADMAP?id=5bf6b86f1b5b12a55305b0dc8030a6f8f2005f01'>doc: Update 'ROADMAP'.</a><span class='msg-avail'>...<span class='msg-tooltip'>Suggested by Omar Radwan &lt;toxemicsquire4@gmail.com&gt;.

* ROADMAP: Rewrite.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2014-01-03 18:19:58 +0100'>2014-01-03</span></td><td><a href='/guix/commit/ROADMAP?id=48ad99db25cf8a60b5d0d3dc333aee89ce8aba8f'>doc: Update 'ROADMAP'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* ROADMAP: Add link to the updated road map, and the a note on release
  history.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2013-01-22 00:17:42 +0100'>2013-01-22</span></td><td><a href='/guix/commit/ROADMAP?id=476f8ea33ce3791dbe0c77332c92e4351827dcd5'>Update `ROADMAP'.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2012-11-18 17:56:02 +0100'>2012-11-18</span></td><td><a href='/guix/commit/ROADMAP?id=b6dd891c1c724906be6a227503ba566def2700c4'>doc: Add `ROADMAP'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* ROADMAP: New file.
* Makefile.am (EXTRA_DIST): Add it.
</span></span></td><td>Ludovic Courtès</td></tr>