Refactor recursive cgroup iteration for killing processes
Refactor recursive cgroup iteration for killing processes

We do this twice and used the same methods for it with boolean
parameters controlling what to do.
But the actual overlap in functionality is smaller than expected
and separating this makes it easier to understand what is happening.

sosy-lab/benchexec,sosy-lab/benchexec,sosy-lab/benchexec,ultimate-pa/benchexec,ultimate-pa/benchexec,ultimate-pa/benchexec,ultimate-pa/benchexec,sosy-lab/benchexec,ultimate-pa/benchexec,ultimate-pa/benchexec,sosy-lab/benchexec,sosy-lab/benchexec