ComparePerf - support to compare various profiles #74

Sometimes we might want to see the difference between different profiles, let's allow to cherry-pick a certain profile and compare it to a different one (currently this is possible by renaming the directory, but it's not really a solution) or even to say just to compare the profiles in a given result (therefore instead of build 1, 2, 3 it's show Localhost, DefaultLibvirt, TunedLibvirt in the table header).