unify lssubsys output

unify lssubsys output

fix several problems in lssubsys output
 * not consistent output with and without -i option
 * without this option lssubsys ignore multiple hierarchies on one mount
point
 * lssubsys -i without -a does not show the hierarchy number

in configuration:
$ cat /proc/cgroups
#subsys_name	hierarchy		num_cgroups		enabled
cpuset	609		1		1
ns		0		1		1
cpu		606		1		1
cpuacct	606		1		1
memory	0		1		1
devices	0		1		1
freezer	612		1		1
net_cls	0		1		1
blkio	0		1		1

Old output:
$ lssubsys
cpu,cpuacct
cpuset,freezer
$ ./lssubsys -i
cpu,cpuacct
cpuset,freezer
$ ./lssubsys -ia
ns
memory
devices
net_cls
blkio
cpuset 609
cpu,cpuacct 606
freezer 612

new one:
$lssubsys
cpuset
cpu,cpuacct
freezer
$ ./lssubsys -i
cpuset 609
cpu,cpuacct 606
freezer 612
$ ./lssubsys -a
ns
memory
devices
net_cls
blkio
cpuset
cpu,cpuacct
freezer

Signed-off-by: Ivana Hutarova Varekova <varekova@redhat.com>
Signed-off-by: Jan Safranek <jsafrane@redhat.com>