history: update user and system cpu usage percent

Updated retroactivly user and system cpu usage percent,
according to the number of cpus of the vm.

Change-Id: Ia47326f94b0b1b696d0bcaf13b5f6df0093b9196
Bug-Url: https://bugzilla.redhat.com/1078897
Signed-off-by: Shirly Radco <sradco@redhat.com>