mpstat: Allow to select individual CPU/nodes with option -A

mpstat: Allow to select individual CPU/nodes with option -A

Previously, using option -A with mpstat would display statistics for all
CPU and nodes (i.e. using -A would also imply -P ALL -N ALL).
Now this is true only if the user didn't specify explicitly a list of
CPU or nodes using options -P or -N.
Example: "mpstat -A -P1,4" will display all possible statistics but only
those concerning CPU 1 and 4 for CPU-related metrics.

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