VPNaaS support for VPN service admin state change and reporting

For VPN service admin state changes, hook up the API call to the service
driver so that the configuration changes can be applied.

Modify the status reporting, so that the VPN service and IPSec
connection status' match the actual status when admin state down
actions are performed (on both the service and connection).

Change-Id: Ife7176675d20bb3ea529a4d79fa92a61f9550a6a
Closes-Bug: 1291609
Merge "VPNaaS support for VPN service admin state change and reporting"