docs: Fix generating qemu-doc.html with texinfo 5

docs: Fix generating qemu-doc.html with texinfo 5

LC_ALL=C makeinfo --no-headers --no-split --number-sections --html qemu-doc.texi -o qemu-doc.html
./qemu-options.texi:1521: unknown command `list'
./qemu-options.texi:1521: table requires an argument: the formatter for @item
./qemu-options.texi:1521: warning: @table has text but no @item

This is for 1.4 stable only; master isn't affected, as it was fixed by
another commit (which isn't appropriate for stable):

commit 5d6768e3b8908a60f0a3016b7fa24194f6b47c80
Author: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Date:   Fri Feb 22 12:39:51 2013 +0900

    sheepdog: accept URIs

Signed-off-by: Cole Robinson <crobinso@redhat.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>