https://issues.apache.org/jira/browse/CLOUDSTACK-730
MASTER, target for 4.3 release.
Add ability to site-to-site VPN to connect between CloudStack virtual routers.
https://cwiki.apache.org/confluence/display/CLOUDSTACK/Site-to-Site+VPN+2.0
1. User creates VPC A and VPC B.
2. User enables VPN gateway on VPC A, and VPC B.
3. User creates VPN customer gateway for VPC A and VPC B.
4. User enables VPN connection on VPC A with customer gateway pointed to VPC B, as "passive".
5. User enables VPN connection on VPC B with customer gateway pointed to VPC A, thus initiate VPN connection.
CreateVpnConnection API:
Add one checkbox "Passive" when creating VPN connection.