Fixup time related units
While trying to solve bug 458277 I ran into a few issues with the time related units.
- Units are doing manual parsing while we have KFormat in KCoreAddons that can do the same.
- UserTime/SystemTime was using an incorrect unit. These are provided by the kernel as "jiffies".
- Total Time was being added as "totalUsage" which meant it was never properly registered.
- Start Time should be using the BootTimestamp unit, but that was deprecated.
This MR fixes all those.
Edited by Arjen Hiemstra