DOC: management: clarify usage of -V with -c

DOC: management: clarify usage of -V with -c

In ticket #3065 an user complained that no success message is printed
anymore when using -c. The message does not appear by default since
version 2.9. This patch clarify the documentation.

Must be backported as far as 2.8.

(cherry picked from commit f4f93c56c17165e7098dc98cecf49e656e57afff)
Signed-off-by: William Lallemand <wlallemand@haproxy.com>
(cherry picked from commit d650878491600e281bf1ea15b378237d28e50b69)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>