vsh: Fix option formatting for 'VHS_OT_ARGV' options

vsh: Fix option formatting for 'VHS_OT_ARGV' options

While previous fixes kept the help output unchanged as base for the
refactors it turns out that the formatting of help for argv options is
wrong.

Specifically in SYNOPSIS the non-positional _ARGV would have the option
name in square brackets (which in other cases means that given thing is
optional) despite being required.

Similarly in the DESCRIPTION section positional versions would not show
the optional argument name and also didn't use the three dots to signal
that it can be used multiple times.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>