[ADD] pull docker image from dockerHub

[clearpal7]

When I created vagrant and I executed the command "blocade up" in a examples/es-cluster directory.
The error was occured like this.

Traceback (most recent call last):
File "/vagrant/blockade/cli.py", line 617, in main
opts.func(opts)
File "/vagrant/blockade/cli.py", line 165, in cmd_up
containers = b.create(verbose=opts.verbose, force=opts.force)
File "/vagrant/blockade/core.py", line 96, in create
container_id = self._start_container(container, force)
File "/vagrant/blockade/core.py", line 174, in _start_container
container_id = create_container()
File "/vagrant/blockade/core.py", line 170, in create_container
labels={"blockade.id": self.state.blockade_id})
File "/usr/local/lib/python2.7/dist-packages/docker-3.7.2-py2.7.egg/docker/api/container.py", line 427, in create_container
return self.create_container_from_config(config, name)
File "/usr/local/lib/python2.7/dist-packages/docker-3.7.2-py2.7.egg/docker/api/container.py", line 438, in create_container_from_config
return self._result(res, True)
File "/usr/local/lib/python2.7/dist-packages/docker-3.7.2-py2.7.egg/docker/api/client.py", line 267, in _result
self._raise_for_status(response)
File "/usr/local/lib/python2.7/dist-packages/docker-3.7.2-py2.7.egg/docker/api/client.py", line 263, in _raise_for_status
raise create_api_error_from_http_exception(e)
File "/usr/local/lib/python2.7/dist-packages/docker-3.7.2-py2.7.egg/docker/errors.py", line 31, in create_api_error_from_http_exception
raise cls(e, response=response, explanation=explanation)
ImageNotFound: 404 Client Error: Not Found ("No such image: sisays/elasticsearch-docker:latest")

Beacause the docker images were pulled only localhost or guest host, so When I pull the elasticsearch docker image was failed.
So I added a line of pulling docker image from dockerHub.