Support for running overlay/overlay2 on a backing filesystem
without d_type support (most likely: xfs, as ext4 supports
this by default), was deprecated for some time.
Running without d_type support is problematic, and can
lead to difficult to debug issues ("invalid argument" errors,
or unable to remove files from the container's filesystem).
This patch turns the warning that was previously printed
into an "unsupported" error, so that the overlay/overlay2
drivers are not automatically selected when detecting supported
storage drivers.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
