util: Extend virProcessGetStatInfo() for sysTime and userTime

util: Extend virProcessGetStatInfo() for sysTime and userTime

The virProcessGetStatInfo() helper parses /proc stat file for
given PID and/or TID and reports cumulative cpuTime which is just
a sum of user and sys times. But in near future, we'll need those
times separately, so make the function return them too (if caller
desires).

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>