Creating PerfEventOutput objects for unavailable CPUs

[jmbass]

Here a PerfEventOutput's created for each CPU configured by the OS, but that doesn't mean the CPU is available.

Boot with nosmt, for example, makes some cores unavailable event if they're configured by the OS. Attempting to open PerfEventOutputs on them results in ENODEV (No such device) errors.

I'm wondering why get_nprocs_conf was used instead of get_nprocs which only returns the number of processors currently available in the system and wether the latter should be used instead.