openconnect v8.10 supports 4 VPN protocols
--protocol=anyconnect Compatible with Cisco AnyConnect SSL VPN, as well as ocserv (default)
--protocol=nc Compatible with Juniper Network Connect
--protocol=gp Compatible with Palo Alto Networks (PAN) GlobalProtect SSL VPN
--protocol=pulse Compatible with Pulse Connect Secure SSL VPN
This patch allows user to specify protocol use the new "vpn_protocol"
option and deprecate the old option "juniper" which seems to be missing in
the current openconnect client.
Signed-off-by: Mengyang Li <mayli.he@gmail.com>