lxcapi_create: don't try to unshare and mount for dir backed containers

It's unnecessary, and breaks unprivileged lxc-create (since unpriv users
cannot yet unshare(CLONE_NEWNS)).

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
add rootfs to container-user args lxccontainer.c: when creating directory backed, don't mount and use the src in place of bdev->dest.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>