In case aufs driver is not supported because supportsAufs() said so,
it is not possible to get a real reason from the logs.
To fix, log the error returned.
Note we're not using WithError here as the error message itself is the
sole message we want to print (i.e. there's nothing to add to it).
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>