mpstat : add -H option to handle vCPU physical hotplug

mpstat : add -H option to handle vCPU physical hotplug

For virtualized environments, physical CPU hotplug can occur.
OR to be more precise vCPU physical hotplug can occur.

Currently, mpstat does not detect physical hotplug when running with an interval.
Example : mpstat -P ALL 5
When -H option is given, display stats of physically hotplugged vCPU also.
Example : mpstat -H -P ALL 5

This is done only when -H option is provided to remain legacy compatible.

Also updated the man page describing the new option.

Signed-off-by: Shaleen Bathla <shaleen.bathla@oracle.com>