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
I don't know how to do this myself...  Is there a consensus about whether or not to change it?   I could also merge this and add a ticket to decide later?