Fetching the repo from github and building clearly does not belong
to runner.py. And probably doesn't belong to anything in mongo-perf, as long
as I clearly expect the user to deal with building process on his own (or
relying on a buildbot). Also, there is *no control at all* for failures in
the build process etc..  Try to follow the KISS principle then, and kick it out
Ideally *all* the mongodb instances should be spawned via the mongomgr
interface, but it looks like a challenge for another day.