client-connect: Implement deferred connect support for plugin API v2

client-connect: Implement deferred connect support for plugin API v2

The V2 API is simpler than the V1 API since there is no passing of
data via files. This also means that with the current API the V2 API
cannot support async notify via files. Adding a file just for async
notify seems very hacky and when needed we should implement a better
option when async is needed for the plugin V2 API.

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20200719173436.16431-5-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg20480.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>