Godeps: update docker-cluster
provision/docker: implement pushImage

This will replace replicateImage.

Related to #708.
provision/docker: do not use redis storage in tests

I've copied mapStorage from docker-cluster. It's way simpler and less
fragile.
provision/docker: fix HealerSuite

Create a custom cluster insteance for the suite, instead of using a
global storage.
provision/docker: do not use alias for import go-dockerclient
provision/docker: fix collector tests
provision/docker: fix test for networkInfo
provision/docker: remove helper function for tests
provision/docker: removing more helper functions

Deleting more and more code. I'm happy today \o/
provision/docker: fix test for pushImage
provision/docker: remove one more helper function from tests