moby/moby commit b27f70d45 wraps the ErrNotFound error returned when
a plugin cannot be found, to include a backtrace. This changes the
type of the error, so contoller.loadIPAMDriver no longer converts it
to a libnetwork plugin.NotFoundError.
This is a similar patch as was merged in 9b114971e5
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>