Initial support for cgroups

Similar to how systemd creates cgroups for all services, for purposes of
tracking, Finit now does the same.  We also mount all available cgroups
in the /sys/fs/cgroup namespace.

This patch adds support for grouping processes in logical cgroups, like
systemd, and an `initctl ps` command to list the hieararchy.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

src/cgreaper.sh

@@ -0,0 +1,11 @@
+#!/bin/sh
+# Called by kernel when last child in cgroup exists
+
+BASE=/sys/fs/cgroup/finit
+PROC=`basename $1`
+DIR="$BASE$1"
+
+logit -p daemon.info -t finit "$PROC stopped, cleaning up control group $DIR"
+rmdir $DIR
+
+exit 0