Merge pull request #25987 from hpcloud/openstack-lbaas-v2

Automatic merge from submit-queue

LBaaS v2 Support for Openstack Cloud Provider Plugin

Resolves #19774.

This work is based on Gophercloud support for LBaaS v2 currently in review (this will have to merge first):
rackspace/gophercloud#575

These changes includes the addition of a new loadbalancer configuration option:  **LBVersion**.  If this configuration attribute is missing or anything other than "v2", lbaas v1 implementation will be used.