MINOR: server: allow cookie for dynamic servers

This commit allows "cookie" keyword for dynamic servers. After code
review, nothing was found which could prevent a dynamic server to use
it. An extra warning is added under cli_parse_add_server() if cookie
value is ignored due to a non HTTP backend.

This patch is not considered a bugfix. However, it may backported if
needed as its impact seems minimal.

(cherry picked from commit 6333e6ec8e35f4e531c46a835fbc0fd121768d32)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit 535f202f570cde43f96c7f35403ada3b3663a217)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
2 files changed