Reference driver implementation (IPsec) for VPNaaS

Implements blueprint ipsec-vpn-reference

This patch implements reference driver implementation for VPNaaS.
The driver uses openswan to manage vpn connections.

Future work: Support ikepolicy and ipsec update
Support service type framework
Intelligent updating of resources

This commit adds jinja2 for requirements.txt for
generating cofig file.

Change-Id: I8c5ed800a71ca014dc7bdbb6a57c4f8d18fa82e0
Merge "Reference driver implementation (IPsec) for VPNaaS"