Some backends can decide not to implement a whole set of APIs (compose
for example), we now return a default implementation that returns a
`errdefs.ErrNotImplemented` for each action making it easy for the cli
to print a helpful error message. We also remove any possible nil
panics.
Signed-off-by: Djordje Lukic <djordje.lukic@docker.com>
Djordje Lukic