The reason is that the generic code which handles reading lxc.rootfs.mount
always frees the old value if not NULL. So without this setting
lxc.rootfs.mount = /mnt causes segfault.

This is a backport for lxc-0.9.0 (dora) of the same fix found in
upstream's master, see commits 54c30e29 and 53f3f048.

Signed-off-by: Josep Puigdemont <josep.puigdemont@enea.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>