lxccontainer: do not display if missing privileges

lxccontainer: do not display if missing privileges

lxc-ls without root privileges on privileged containers should not display
information. In lxc_container_new(), ongoing_create()'s result is not checked
for all possible returned values. Hence, an unprivileged user can send command
messages to the container's monitor. For example:

$ lxc-ls -P /.../tests -f
NAME     STATE AUTOSTART GROUPS IPV4 IPV6 UNPRIVILEGED
ctr -     0         -      -    -    false
$ sudo lxc-ls -P /.../tests -f
NAME     STATE   AUTOSTART GROUPS IPV4      IPV6 UNPRIVILEGED
ctr RUNNING 0         -      10.0.3.51 -    false

After this change:

$ lxc-ls -P /.../tests -f      <-------- No more display without root privileges
$ sudo lxc-ls -P /.../tests -f
NAME     STATE   AUTOSTART GROUPS IPV4      IPV6 UNPRIVILEGED
ctr RUNNING 0         -      10.0.3.37 -    false
$

Signed-off-by: Rachid Koucha <rachid.koucha@gmail.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>