bdev: use correct overlay module name
bdev: use correct overlay module name

- Assume that the module name is "overlay" per default and not "overlayfs".
- Assume that the overlay version we are using requires a workdir.
- When we mount an overlay filesystem and we fail with ENODEV retry once with
  the module name we haven't already used.

Signed-off-by: Christian Brauner <b487c2d908f9548b106d14dc6d7b88a1fc58d1d6@suse.de>

lxc/lxc-pkg-ubuntu,lxc/lxc-pkg-ubuntu,lxc/lxc-pkg-ubuntu