sadf: PSI: Change metrics names and make them percent values

sadf: PSI: Change metrics names and make them percent values

Change PSI metrics names (e.g. s_acpu10 -> %scpu-10) to make clear that
they are percent values.
Also change metrics using the total number of microseconds spent stalled
on ressources to also be a percent value calculated over the past time
interval (e.g. s_tcpu/s -> %scpu).

Signed-off-by: Sebastien GODARD <sysstat@users.noreply.github.com>