browsermob-proxy role added

@jzoldak Please review.  Should someone from devops review this as well?


related to https://github.com/edx/bok-choy/pull/53 and https://github.com/edx/edx-platform/pull/4640
Yes, I believe that s3 bucket is associated with the [official maintainer of the plugin](https://github.com/lightbody/browsermob-proxy). I think either way would be fine.