For example the following sequence is expected to work:

lxc-start -n containerName -f /path/to/conf \
-s 'lxc.id_map = u 0 100000 65536' \
-s 'lxc.id_map = g 0 100000 65536' \
-s 'lxc.rootfs = /path/to/rootfs' \
-s 'lxc.init_cmd = /path/to/initcmd'

lxc-attach -n containerName

Closes #984.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>