Add management client version

Add management client version

- "version" command from client to management can now set
  the version of management interface supported by the client
  by specifying an optional integer parameter.

  If no parameter is specified the version of OpenVPN
  and its management interface is returned (current behaviour).

  The client version defaults to 1 which is the current version of
  the Management Interface.

Signed-off-by: Selva Nair <selva.nair@gmail.com>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <1516909261-31623-1-git-send-email-selva.nair@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg16363.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>