Add volume mapping support and `LogstreamerInput`.
Map container volumes to host volumes.
Log collection tweaks.
Syncing up with `master`.
Improve Heka log collection.

* Substitute environment variables in mapped volume names.
* Use separate Heka and log directories for each run.
* Tag Heka messages with the collection ID, run ID, and AWS hostname.
* Handle sequential service logs.
* Include the AWS instance ID in statsd metric names.
Flush cAdvisor stats based on the test run time.
Syncing up with `master`.
Revert to the default InfluxDB stat encoder.
Add `DockerLogInput`.
Syncing up with `master`.
Remove logging changes.
Merge pull request #13 from loads/feature/volumes

Add volume mapping support