Otherwise udev can unecessarily execute various rules (and issue
scanning IO, etc) against the thin-pool -- which can never be a
top-level device.
Docker-DCO-1.1-Signed-off-by: Mike Snitzer <snitzer@redhat.com> (github: snitm)
Upstream-commit: ad6467f9e17205fa76a3b916efe51ba5c1b37506
Component: engine