openconnect: add recipe

openconnect is a FOSS VPN client designed to work with Cisco AnyConnect
and Pulse Connect Secure (Juniper SSL).

Signed-off-by: Ioan-Adrian Ratiu <adrian.ratiu@ni.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>
Signed-off-by: Armin Kuster <akuster808@gmail.com>