Add VPNaaS plugin codes for Quantum
* can add/update/delete/search site configure to/from SQL db
* can POST/PUT/DELETE/GET site(s) configure from REST API
* run_test.py db.vpn.test_db_vpn:TestVPNXML is passed
* TBD, configure path to VSE is not cover in this change
* TBD, should add support for isakmp_policy, ipsec_policy, trust_profile support