Launch cAdvisor and Heka containers

This pull request adds support for cAdvisor and Heka: `EC2Collection#wait_for_docker()` pulls the corresponding containers, `#start()` launches the containers prior to running the test, and `#stop()` shuts down the containers.

* Add `--influx-{host, port, user, password}` and `---heka-{host, port}` flags.
* Add support for volume and port bindings to `DockerDaemon#run_container()`.
* Add `EC2Instance#stop{cadvisor, heka}()`.
* Add `ssh.makedirs()`.

I tried to match the existing code style and idioms, but there's probably a lot of room for improvement. :smiley: I also haven't updated the tests yet, but verified this against a set of EC2 instances.

@bbangert r?
Heka can run a dashboard, seeing that it returns a 200 to the HTTP call would be the easiest way to verify that heka is running (I think). Though we'd have to open the HTTP port to easily check it without using an ssh tunnel.