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
All other things being equal, I'd recommend choosing the path of least resistance.
I.e. use theirs and if we need to change it later we can.
:)