Parameterize branch in etc/perf.yml

We use different directories in perf.yml based on the branch. For instance, 3.2 uses perf-3.2. We should generalize or parameterize the path in perf.yml so we don't have to hard code in the branch version.

For example this line in 3.2:

       remote_file: perf-3.2/${version_id}/${revision}/mongod-${version_id}

And the matching line in master

        remote_file: perf/${version_id}/${revision}/mongod-${version_id}

Both should be replaced with something like

${project}

or

perf-${branch}