We use $(grep -c ^processor /proc/cpuinfo) as the -j/num_jobs_available value for ubuntu1604-arm64 distros right now.
As we're about to get new high core build ARM servers, we should limit the num_jobs_available because some test might fail when the value is too high (nobody runs 96 mongod instances on a single server in a real setup).

We should do it in such way that this would work on both new and old servers.