Added new hypervisor to support Docker containers

Docker brings an alternative to support Linux Containers (LXC)
as instances. The code has been imported from:
https://github.com/dotcloud/openstack-docker

blueprint new-hypervisor-docker

Change-Id: I0f1ff8acb5a93ba1dc680c68633c43454d1e804c
Merge "Added new hypervisor to support Docker containers"