Add the docker container start flag

[bhuisgen]

This PR allows to create only a container without starting it after creation (it will start at next reboot depending of the restart policy).

resource "docker_image" "foo" {
	name = "nginx:latest"
}

resource "docker_container" "foo" {
	name = "tf-test"
	image = "${docker_image.foo.latest}"
	start = false
        must_run = false
}

[mavogel]

hey @bhuisgen, thx for another contribution :) could you take a look at the failing tests and fix them