cloud: docker deployment support

Cloud properties:

  cloud.provider=docker
  cloud.base_url=unix://var/run/docker.sock
  cloud.vm_name=container_name
  cloud.image=image_name
  'cloud.binds:-json={"/sys/fs/cgroup": {"bind": "/sys/fs/cgroup", "ro": true}}'
  cloud.dns=10.0.0.1
  cloud.privileged:bool=true

Docker base_url can also be set vi env varible:

  export DOCKER_BASE_URL=unix://var/run/docker.sock