lxc-ls: Allow the use of --groups without --fancy

There wasn't a good reason for that limit, we can simply make the code
slightly slower when --groups is passed and still have the expected
output even without --fancy.

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
cgfs: don't mount /sys/fs/cgroup readonly

/sys/fs/cgroup is just a size-limited tmpfs, and making it ro does
nothing to affect our ability alter mount settings of its subdirs.
OTOH making it ro can upset mountall in the container which tries
to remount it rw, which may be refused.

So just don't do it.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Cc: Christian Seiler <christian@iwakd.de>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>
doc: Update Japanese lxc-ls(1) for the new -g/--group argument

Update for commit 0f02786

Signed-off-by: KATOH Yasufumi <karma@jazz.email.ne.jp>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>