RFC: lxclock: drop the chown+chmod of lockdir

The original rationale for this was to make sure that if
lxcpath was /home/serge/lxcbase, then then lockdir
(/run/user/serge/lock/lxc/home/serge/lxcbase) would be
owned by the same user as /home/serge/lxcbase.

The only user who can chown to other uids (without CAP_CHOWN
added to fP) is root, who shouldn't be mucking with non-root
owned containers anyway.  In the meantime this causes a bunch
of noise for arguably no benefit.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
refactor string conf items into common function

- When doing the selinux change, I noticed that there was a lot of
  duplication of code in handing string configuration items, so I
  refactored this into a common function.

- Added a config_string_max that can be passed a maximum acceptable
  length, used to limit ttydir to NAME_MAX.

- The behavior of config_seccomp was different than other strings: if the
  item was already defined, then the second attempt to set it would fail
  instead of just replacing the value. Changed to just replace the value.

- Remove unused key and lxc_conf arguments to config_path_item().

Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>
Signed-off-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>