FdbTop: fixed display of hdd and cpu utilization

- each process can use a different hdd so it is not currently possible to show a combine hdd %busy for the machine
- machine cpu 1 means that ALL logical threads are UsedBytes
- process cpu 1 means one logical thread is used (a process can use a little bit more)
FdbBurner: added keys to change value size and local disk perf counters

- note: local disk perf counters only work is using local fdb server, and only for disk C: