add api for generating the list of all controllers (not only mount ones)

add api for generating the list of all controllers (not only mount ones)

this patch add api for generating the list of all controllers (not only mount ones)
- it uses three functions:
cgroup_get_all_controller_begin
cgroup_get_all_controller_next
cgroup_get_all_controller_end

and structure:
struct controller_data {
		char name[FILENAME_MAX];
		int hierarchy;
		int num_cgroups;
		int enabled;
};

the data are read from /proc/cgroups file

Signed-off-by: Ivana Hutarova Varekova <varekova@redhat.com>
Reviewed-by: Jan Safranek <jsafrane@redhat.com>
Signed-off-by: Dhaval Giani <dhaval@linux.vnet.ibm.com>