qapi2texi: Fix up output around #optional

qapi2texi: Fix up output around #optional

We use tag #optional to mark optional members, like this:

    # @name: #optional The name of the guest

texi_body() strips #optional, but not whitespace around it.  For the
above, we get in qemu-qmp-qapi.texi

    @item @code{'name'} (optional)
     The name of the guest
    @end table

The extra space can lead to artifacts in output, e.g in
qemu-qmp-ref.7.pod

    =item C<'name'> (optional)

     The name of the guest

and then in qemu-qmp-ref.7

    .IX Item "name (optional)"
    .Vb 1
    \& The name of the guest
    .Ve

instead of intended plain

    .IX Item "name (optional)"
    The name of the guest

Get rid of these artifacts by removing whitespace around #optional
along with it.

This turns three minus signs in qapi-schema.json into markup, because
they're now at the beginning of the line.  Drop them, they're unwanted
there.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <1489582656-31133-11-git-send-email-armbru@redhat.com>