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.