Set CPU governor properly on linux benchmarks

cpu* was used to select all CPUs, but this incorrectly selects 
folders such as cpufreq and cpuidle, which you cannot set a 
governor on. Therefore this call not only always failed, but 
actually stopped the other tuning calls from running. The 
proper wildcard should only select folders named 
cpu[number], so I've used cpu[0-9]. This may silently fail if
someone has more than 10 CPUs e.g. cpu14, perhaps there's a 
bash wildcard option to allow [0-9]*?