IPSec strongSwan VPNaaS Driver

Provide one choice for ubuntu customers to run strongSwan
ipsec vpn on it just as openswan does on Redhat.

Change-Id: I063fd81e29abb1b72c519606c2c9238811c0515d
Implements: blueprint ipsec-strongswan-driver
Merge "IPSec strongSwan VPNaaS Driver"