`run_container`: Add support for port bindings.
`EC2Instance`: Reuse SSH and SFTP connections.
Launch Heka containers. Refactor options handling.

* Add `{Heka, Influx}Options`.
* Add `--heka-{host, port}` flags.
* Publish the Heka and cAdvisor ports for container status checks.
* Move `start_{cadvisor, heka}()` into `EC2Instance`.
* Add `EC2Instance#stop{cadvisor, heka}()`. Ensure `EC2Collection`
  stops Heka and cAdvisor on test completion.
* Add `EC2Instance#makedirs()` for recursively creating remote
  directories.
* `EC2Collection#wait_for_docker()` now only waits for Heka and
  cAdvisor to become available. `#start()` launches the containers.