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/finit.c

@@ -36,6 +36,7 @@
 #include <lite/lite.h>
 
 #include "finit.h"
+#include "cgroup.h"
 #include "cond.h"
 #include "conf.h"
 #include "helpers.h"
@@ -352,6 +353,11 @@ int main(int argc, char* argv[])
 	if (fisdir("/proc/bus/usb"))
 		mount("none", "/proc/bus/usb", "usbfs", 0, NULL);
 
+	/*
+	 * Initialize default control groups, if available
+	 */
+	cgroup_init();
+
 	/*
 	 * Parse kernel command line (debug, rescue, splash, etc.)
 	 * Also calls log_init() to set correct log level